diff --git a/config.inc.php.example b/config.inc.php.example
index 47e314e..a8aa847 100644
--- a/config.inc.php.example
+++ b/config.inc.php.example
@@ -15,6 +15,7 @@ $usecache           = false; # use cache ? {true,false}
 $dir_cache          = dirname(__FILE__) .'/cache/'; # directory where cache files will be stored
 $cleanurls          = false; # Use mod_rewrite to hide PHP extensions {true,false[default]}
 			     # be cautious, doesn't work for all hosts, you may need to modify the .htaccess file
+$debugMode			= false; # if true, show debug messages			     
 
 #### Database ####
 $dbtype = 'mysql4'; # Database driver {mysql, mysqli, mysql4, oracle, postgres, sqlite, db2, firebird, mssql, mssq-odbc}
@@ -85,5 +86,5 @@ $menu2Tags = array('example', 'of', 'menu', 'tags'); # list of tags used by menu
 $sizeSearchHistory = 10; # number of users' searches that are saved {1..10[Default]..-1[Unlimited]}
 $enableGoogleCustomSearch = true; #Enable Google Search Engine into "gsearch/" folder
 
-include_once('debug.inc.php');
+
 ?>
diff --git a/constants.inc.php b/constants.inc.php
index 824561f..e779852 100644
--- a/constants.inc.php
+++ b/constants.inc.php
@@ -1,4 +1,30 @@
 <?php
+/*
+ * Define constants use in all the application.
+ * Some constants are based on variables from configuration file.
+ */
+
+// Debug managament
+if(isset($GLOBALS['debugMode'])) {
+	define('DEBUG_MODE', $GLOBALS['debugMode']);
+	define('DEBUG_EXTRA', $GLOBALS['debugMode']); // Constant used exclusively into db/ directory
+}
+
+// Determine the base URL as ROOT
+if (!isset($GLOBALS['root'])) {
+	$pieces = explode('/', $_SERVER['SCRIPT_NAME']);
+	$rootTmp = '/';
+	foreach($pieces as $piece) {
+		if ($piece != '' && !strstr($piece, '.php')) {
+			$rootTmp .= $piece .'/';
+		}
+	}
+	if (($rootTmp != '/') && (substr($rootTmp, -1, 1) != '/')) {
+		$rootTmp .= '/';
+	}
+
+	define('ROOT', 'http://'. $_SERVER['HTTP_HOST'] . $rootTmp);
+}
 
 // Error codes
 define('GENERAL_MESSAGE', 200);
@@ -19,7 +45,7 @@ define('INSTALLATION_ID', md5($GLOBALS['dbname'].$GLOBALS['tableprefix']));
 
 // Correct bug with PATH_INFO (maybe for Apache 1)
 if(strlen($_SERVER["PATH_INFO"])<strlen($_SERVER["ORIG_PATH_INFO"])) {
-    $_SERVER["PATH_INFO"] = $_SERVER["ORIG_PATH_INFO"]; 
+	$_SERVER["PATH_INFO"] = $_SERVER["ORIG_PATH_INFO"];
 }
 
 ?>
diff --git a/debug.inc.php b/debug.inc.php
deleted file mode 100644
index 8bd7f33..0000000
--- a/debug.inc.php
+++ /dev/null
@@ -1,16 +0,0 @@
-<?php
-// Turn debugging on
-define('SCUTTLE_DEBUG',true);
-
-// generic debugging function
-// Sample:
-//     pc_debug(__FILE__, __LINE__, "This is a debug message.");
-
-function pc_debug($file, $line, $message) {
-    if (defined('SCUTTLE_DEBUG') && SCUTTLE_DEBUG) {
-        error_log("---DEBUG-". $sitename .": [$file][$line]: $message");
-    } else {
-        error_log("SCUTTLE_DEBUG disabled");
-    }
-}
-?>
\ No newline at end of file
diff --git a/functions.inc.php b/functions.inc.php
index 35f0fed..93821fd 100644
--- a/functions.inc.php
+++ b/functions.inc.php
@@ -85,11 +85,11 @@ function multi_array_search($needle, $haystack) {
 }
 
 function createURL($page = '', $ending = '') {
-    global $cleanurls, $root;
+    global $cleanurls;
     if (!$cleanurls && $page != '') {
         $page .= '.php';
     }
-    return $root . $page .'/'. $ending;
+    return ROOT . $page .'/'. $ending;
 }
 
 /* Shorten a string like a URL for example by cutting the middle of it */
@@ -112,7 +112,7 @@ function message_die($msg_code, $msg_text = '', $msg_title = '', $err_line = '',
 	
 	// Get SQL error if we are debugging. Do this as soon as possible to prevent 
 	// subsequent queries from overwriting the status of sql_error()
-	if (DEBUG && ($msg_code == GENERAL_ERROR || $msg_code == CRITICAL_ERROR)) {
+	if (DEBUG_MODE && ($msg_code == GENERAL_ERROR || $msg_code == CRITICAL_ERROR)) {
 		$sql_error = is_null($db) ? '' : $db->sql_error();
 		$debug_text = '';
 		
@@ -157,10 +157,10 @@ function message_die($msg_code, $msg_text = '', $msg_title = '', $err_line = '',
 			break;
 	}
 
-	// Add on DEBUG info if we've enabled debug mode and this is an error. This
-	// prevents debug info being output for general messages should DEBUG be
+	// Add on DEBUG_MODE info if we've enabled debug mode and this is an error. This
+	// prevents debug info being output for general messages should DEBUG_MODE be
 	// set TRUE by accident (preventing confusion for the end user!)
-	if (DEBUG && ($msg_code == GENERAL_ERROR || $msg_code == CRITICAL_ERROR)) {
+	if (DEBUG_MODE && ($msg_code == GENERAL_ERROR || $msg_code == CRITICAL_ERROR)) {
 		if ($debug_text != '')
 			$msg_text = $msg_text . '<br /><br /><strong>'. T_('DEBUG MODE') .'</strong>'. $debug_text;
 	}
diff --git a/gsearch/context.php b/gsearch/context.php
index a48179f..1a65063 100644
--- a/gsearch/context.php
+++ b/gsearch/context.php
@@ -14,7 +14,7 @@
         </LookAndFeel>
     </CustomSearchEngine>
 
-    <Include type="Annotations" href="<?php echo $GLOBALS['root'];?>api/export_gcs.php?xml=1" />
+    <Include type="Annotations" href="<?php echo ROOT;?>api/export_gcs.php?xml=1" />
 
 
 </GoogleCustomizations>
diff --git a/gsearch/index.php b/gsearch/index.php
index d4f596d..e7011bf 100644
--- a/gsearch/index.php
+++ b/gsearch/index.php
@@ -14,7 +14,7 @@ if($GLOBALS['enableGoogleCustomSearch']==false) {
 
 <!-- Google CSE Search Box Begins  -->
 <form id="cref" action="http://www.google.com/cse">
-  <input type="hidden" name="cref" value="<?php echo $GLOBALS['root']?>gsearch/context.php" />
+  <input type="hidden" name="cref" value="<?php echo ROOT;?>gsearch/context.php" />
   <input type="text" name="q" size="40" />
   <input type="submit" name="sa" value="Search" />
 </form>
diff --git a/header.inc.php b/header.inc.php
index 820b5f9..f94ce0d 100644
--- a/header.inc.php
+++ b/header.inc.php
@@ -1,35 +1,31 @@
 <?php
-ini_set('display_errors', '1');
-ini_set('mysql.trace_mode', '0');
-
-error_reporting(E_ALL ^ E_NOTICE);
-//error_reporting(E_ALL);
-
-define('DEBUG', true);
-session_start();
-
 if(!file_exists(dirname(__FILE__) .'/config.inc.php')) {
-    die("Please, create the 'config.inc.php' file. You can copy the 'config.inc.php.example' file.");
+	die("Please, create the 'config.inc.php' file. You can copy the 'config.inc.php.example' file.");
 }
 
-require_once(dirname(__FILE__) .'/services/servicefactory.php');
+// First requirements part (before debug management)
 require_once(dirname(__FILE__) .'/config.inc.php');
-require_once(dirname(__FILE__) .'/constants.inc.php');
+require_once(dirname(__FILE__) .'/constants.inc.php'); // some constants are based on variables from config file
+
+
+// Debug Management using constants
+if(DEBUG_MODE) {
+	ini_set('display_errors', '1');
+	ini_set('mysql.trace_mode', '1');
+	error_reporting(E_ALL);
+	//error_reporting(E_ALL^E_NOTICE);
+} else {
+	ini_set('display_errors', '0');
+	ini_set('mysql.trace_mode', '0');
+	error_reporting(0);
+}
+
+
+// Second requirements part which could display bugs (must come after debug management)
+require_once(dirname(__FILE__) .'/services/servicefactory.php');
 require_once(dirname(__FILE__) .'/functions.inc.php');
 
-// Determine the base URL
-if (!isset($root)) {
-    $pieces = explode('/', $_SERVER['SCRIPT_NAME']);
-    $root = '/';
-    foreach($pieces as $piece) {
-        if ($piece != '' && !strstr($piece, '.php')) {
-            $root .= $piece .'/';
-        }
-    }
-    if (($root != '/') && (substr($root, -1, 1) != '/')) {
-        $root .= '/';
-    }
-    $root = 'http://'. $_SERVER['HTTP_HOST'] . $root;
-}
+
+session_start();
 
 ?>
diff --git a/index.php b/index.php
index 2b5eda2..0a2b483 100644
--- a/index.php
+++ b/index.php
@@ -20,6 +20,7 @@
  ***************************************************************************/
 
 require_once('header.inc.php');
+
 $bookmarkservice =& ServiceFactory::getServiceInstance('BookmarkService');
 $templateservice =& ServiceFactory::getServiceInstance('TemplateService');
 $userservice =& ServiceFactory::getServiceInstance('UserService');
diff --git a/jsScuttle.php b/jsScuttle.php
index 53356aa..222b91d 100644
--- a/jsScuttle.php
+++ b/jsScuttle.php
@@ -2,7 +2,7 @@
 header('Content-Type: text/javascript');
 require_once('header.inc.php');
 require_once('functions.inc.php');
-$player_root = $root .'includes/player/';
+$player_root = ROOT .'includes/player/';
 ?>
 
 function _playerAdd(anchor) {
@@ -41,7 +41,7 @@ function deleteConfirmed(ele, input, response) {
         post.style.display = 'none';
         deleted = false;
     } else {
-        loadXMLDoc('<?php echo $root; ?>ajaxDelete.php?id=' + input);
+        loadXMLDoc('<?php echo ROOT; ?>ajaxDelete.php?id=' + input);
         post.style.display = 'none';
         
     }
@@ -62,7 +62,7 @@ function isAvailable(input, response){
     username = username.trim();
     var availability = document.getElementById("availability");
     if (username != '') {
-        usernameField.style.backgroundImage = 'url(<?php echo $root; ?>images/loading.gif)';
+        usernameField.style.backgroundImage = 'url(<?php echo ROOT; ?>images/loading.gif)';
         if (response != '') {
             usernameField.style.backgroundImage = 'none';
             if (response == 'true') {
@@ -73,7 +73,7 @@ function isAvailable(input, response){
                 availability.innerHTML = '<?php echo T_('Not Available'); ?>';
             }
         } else {
-            loadXMLDoc('<?php echo $root; ?>ajaxIsAvailable.php?username=' + username);
+            loadXMLDoc('<?php echo ROOT; ?>ajaxIsAvailable.php?username=' + username);
         }
     }
 }
@@ -92,12 +92,12 @@ function useAddress(ele) {
 function getTitle(input, response){
     var title = document.getElementById('titleField');
     if (title.value == '') {
-        title.style.backgroundImage = 'url(<?php echo $root; ?>images/loading.gif)';
+        title.style.backgroundImage = 'url(<?php echo ROOT; ?>images/loading.gif)';
         if (response != null) {
             title.style.backgroundImage = 'none';
             title.value = response;
         } else if (input.indexOf('http') > -1) {
-            loadXMLDoc('<?php echo $root; ?>ajaxGetTitle.php?url=' + input);
+            loadXMLDoc('<?php echo ROOT; ?>ajaxGetTitle.php?url=' + input);
         } else {
             return false;
         }
diff --git a/rss.php b/rss.php
index fc35e40..476a28d 100644
--- a/rss.php
+++ b/rss.php
@@ -75,7 +75,7 @@ if ($cat) {
 }
 
 $tplVars['feedtitle'] = filter($GLOBALS['sitename'] . (isset($pagetitle) ? $pagetitle : ''));
-$tplVars['feedlink'] = $GLOBALS['root'];
+$tplVars['feedlink'] = ROOT;
 $tplVars['feeddescription'] = sprintf(T_('Recent bookmarks posted to %s'), $GLOBALS['sitename']);
 
 $bookmarks =& $bookmarkservice->getBookmarks(0, 15, $userid, $cat, NULL, getSortOrder(), $watchlist);
diff --git a/services/userservice.php b/services/userservice.php
index 9b295da..e611cb8 100644
--- a/services/userservice.php
+++ b/services/userservice.php
@@ -23,8 +23,8 @@ class UserService {
         function UserService(& $db) {
         	$this->db =& $db;
         	$this->tablename = $GLOBALS['tableprefix'] .'users';
-        	$this->sessionkey = $GLOBALS['cookieprefix'].INSTALLATION_ID.'-currentuserid';
-        	$this->cookiekey = $GLOBALS['cookieprefix'].INSTALLATION_ID.'-login';
+        	$this->sessionkey = INSTALLATION_ID.'-currentuserid';
+        	$this->cookiekey = INSTALLATION_ID.'-login';
         	$this->profileurl = createURL('profile', '%2$s');
         }
 
@@ -124,10 +124,11 @@ class UserService {
         	if (!is_null($newval)) //internal use only: reset currentuser
         	$currentuser = $newval;
         	else if ($refresh || !isset($currentuser)) {
-        		if ($id = $this->getCurrentUserId())
-        		$currentuser = $this->getUser($id);
-        		else
-        		return null;
+        		if ($id = $this->getCurrentUserId()) {
+        			$currentuser = $this->getUser($id);
+        		} else {
+        			$currentuser = null;
+        		}
         	}
         	return $currentuser;
         }
diff --git a/templates/bookmarks.tpl.php b/templates/bookmarks.tpl.php
index 27dfb6e..5567d7b 100644
--- a/templates/bookmarks.tpl.php
+++ b/templates/bookmarks.tpl.php
@@ -257,7 +257,7 @@ window.onload = playerLoad;
     $brss = '';
     $size = count($rsschannels);
     for ($i = 0; $i < $size; $i++) {
-        $brss =  '<a style="background:#FFFFFF" href="'. $rsschannels[$i][1] .'" title="'. $rsschannels[$i][0] .'"><img src="'. $GLOBALS['root'] .'images/rss.gif" width="16" height="16" alt="'. $rsschannels[$i][0] .'" /></a>'; 
+        $brss =  '<a style="background:#FFFFFF" href="'. $rsschannels[$i][1] .'" title="'. $rsschannels[$i][0] .'"><img src="'. ROOT .'images/rss.gif" width="16" height="16" alt="'. $rsschannels[$i][0] .'" /></a>'; 
     }
 
     echo '<p class="paging">'. $bfirst .'<span> / </span>'. $bprev .'<span> / </span>'. $bnext .'<span> / </span>'. $blast .'<span> / </span>'. sprintf(T_('Page %d of %d'), $page, $totalpages) ." ". $brss ." </p>\n";
diff --git a/templates/editbookmark.tpl.php b/templates/editbookmark.tpl.php
index f6affc4..c947ec3 100644
--- a/templates/editbookmark.tpl.php
+++ b/templates/editbookmark.tpl.php
@@ -43,7 +43,7 @@ switch ($row['bStatus']) {
 <tr>
     <th align="left"><?php echo T_('Tags'); ?></th>
     <td class="scuttletheme">
-    <span dojoType="dojo.data.ItemFileReadStore" jsId="memberTagStore" url="<?php echo $GLOBALS['root']?>ajax/gettags.php"></span>
+    <span dojoType="dojo.data.ItemFileReadStore" jsId="memberTagStore" url="<?php echo ROOT?>ajax/gettags.php"></span>
     <input type="text" dojoType="dojox.form.MultiComboBox" id="tags" name="tags" size="75" value="<?php echo filter(implode(', ', $row['tags']), 'xml'); ?>" store="memberTagStore" delimiter="," searchAttr="tag" hasDownArrow="false"/></td>
     <td>&larr; <?php echo T_('Comma-separated'); ?></td>
 </tr>
diff --git a/templates/login.tpl.php b/templates/login.tpl.php
index 6137dc0..def2d72 100644
--- a/templates/login.tpl.php
+++ b/templates/login.tpl.php
@@ -27,7 +27,7 @@ window.onload = function() {
         <td></td>
     </tr>
     </table>
-    <p>&raquo; <a href="<?php echo $GLOBALS['root'] ?>password.php"><?php echo T_('Forgotten your password?') ?></p>
+    <p>&raquo; <a href="<?php echo ROOT ?>password.php"><?php echo T_('Forgotten your password?') ?></p>
 </form>
 
 <?php
diff --git a/templates/sidebar.block.recent.php b/templates/sidebar.block.recent.php
index a128e70..fef85f2 100644
--- a/templates/sidebar.block.recent.php
+++ b/templates/sidebar.block.recent.php
@@ -20,11 +20,12 @@ if ($recentTags && count($recentTags) > 0) {
     <?php
     $contents = '<p class="tags">';
 
-    if(strlen($user)==0) {
-	$cat_url = createURL('tags', '%2$s');
+    if(!isset($user)) {
+    	$user = '';
+		$cat_url = createURL('tags', '%2$s');
     }
 
-    foreach ($recentTags as $row) {
+    foreach ($recentTags as $row) {    	
         $entries = T_ngettext('bookmark', 'bookmarks', $row['bCount']);
         $contents .= '<a href="'. sprintf($cat_url, $user, filter($row['tag'], 'url')) .'" title="'. $row['bCount'] .' '. $entries .'" rel="tag" style="font-size:'. $row['size'] .'">'. filter($row['tag']) .'</a> ';
     }
diff --git a/templates/toolbar.inc.php b/templates/toolbar.inc.php
index 92d8d59..0b052e0 100644
--- a/templates/toolbar.inc.php
+++ b/templates/toolbar.inc.php
@@ -13,7 +13,7 @@ if ($userservice->isLoggedOn()) {
         <li><a href="<?php echo createURL('watchlist', $cUsername); ?>"><?php echo T_('Watchlist'); ?></a></li>
 	<li><a href="<?php echo $userservice->getProfileUrl($cUserId, $cUsername); ?>"><?php echo T_('Profile'); ?></a></li>
         <li><a href="<?php echo createURL('bookmarks', $cUsername . '?action=add'); ?>"><?php echo T_('Add a Bookmark'); ?></a></li>
-        <li class="access"><?php echo $cUsername?><a href="<?php echo $GLOBALS['root']; ?>?action=logout">(<?php echo T_('Log Out'); ?>)</a></li>
+        <li class="access"><?php echo $cUsername?><a href="<?php echo ROOT ?>?action=logout">(<?php echo T_('Log Out'); ?>)</a></li>
         <li><a href="<?php echo createURL('about'); ?>"><?php echo T_('About'); ?></a></li>
 	<?php if($isAdmin): ?>
         <li><a href="<?php echo createURL('admin', ''); ?>"><?php echo '['.T_('Admin').']'; ?></a></li>
diff --git a/templates/top.inc.php b/templates/top.inc.php
index 88a949a..0d59dfb 100644
--- a/templates/top.inc.php
+++ b/templates/top.inc.php
@@ -5,9 +5,9 @@
 <title><?php echo filter($GLOBALS['sitename'] . (isset($pagetitle) ? ': ' . $pagetitle : '')); ?></title>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
 <link rel="icon" type="image/png"
-	href="<?php echo $GLOBALS['root']; ?>icon.png" />
+	href="<?php echo ROOT ?>icon.png" />
 <link rel="stylesheet" type="text/css"
-	href="<?php echo $GLOBALS['root']; ?>scuttle.css" />
+	href="<?php echo ROOT ?>scuttle.css" />
 <?php
 if(isset($rsschannels)) {
 	$size = count($rsschannels);
@@ -20,7 +20,7 @@ if(isset($rsschannels)) {
 <?php if (isset($loadjs)) :?>
 
 <script type="text/javascript"
-	src="<?php echo $GLOBALS['root']; ?>jsScuttle.php"></script>
+	src="<?php echo ROOT ?>jsScuttle.php"></script>
 
 <link rel="stylesheet" type="text/css"
 	href="http://ajax.googleapis.com/ajax/libs/dojo/1.2/dijit/themes/nihilo/nihilo.css">
@@ -50,7 +50,7 @@ if(isset($_GET['popup'])) {
 ?>
 
 <div id="header" <?php echo $headerstyle; ?>>
-<h1><a href="<?php echo $GLOBALS['root']; ?>"><?php echo $GLOBALS['sitename']; ?></a></h1>
+<h1><a href="<?php echo ROOT ?>"><?php echo $GLOBALS['sitename']; ?></a></h1>
 <?php
 if(!isset($_GET['popup'])) {
 	$this->includeTemplate('toolbar.inc');
diff --git a/upgrade.txt b/upgrade.txt
index 6b54428..acf6a96 100644
--- a/upgrade.txt
+++ b/upgrade.txt
@@ -1,9 +1,19 @@
 ==== UPGRADE instructions ====
 
+
+=== From version 0.90 to 0.91 ===
+- Backup you database
+- Make a copy from your SemanticScuttle Web directory
+- Upgrade your database by following instructions ONE after ONE (order is important) :
+  * No intructions
+- Upgrade your current configuration file (config.inc.php) with respect to config.inc.php.example
+  * Delete last line : include_once('debug.inc.php');
+  * Add variable: $menu2Tags = array();
+  * Add variable: $debugMode = true; # if true, show debug messages
+
 === From version 0.89 to 0.90 ===
 - Backup you database
 - Make a copy from your SemanticScuttle Web directory
-- Upgrade your database by following instructions ONE after ONE (order is important) :
 
 - Upgrade your current configuration file (config.inc.php) with respect to config.inc.php.example
 # add these lines under $enableWebsiteThumbnails = false; # enableWebsiteThumbnails {true|false}: