Index: moodle/auth/shibboleth/logout.php
===================================================================
--- moodle/auth/shibboleth/logout.php	(revision 3897)
+++ moodle/auth/shibboleth/logout.php	(working copy)
@@ -125,10 +125,11 @@
     global $CFG, $SESSION, $DB;
 
     // Delete session of user using $SessionID
-    if(empty($CFG->dbsessions)) {
+    $session_class = $CFG->session_handler_class;
+    if(preg_match('/file/i', $session_class) === 1) {
 
         // File session
-        $dir = $CFG->dataroot .'/sessions';
+        $dir = $CFG->session_file_save_path;
         if (is_dir($dir)) {
             if ($dh = opendir($dir)) {
                 // Read all session files
@@ -159,7 +160,7 @@
                 closedir($dh);
             }
         }
-    } else {
+    } elseif(preg_match('/database/i', $session_class) === 1) {
         // DB Session
         //TODO: this needs to be rewritten to use new session stuff
         if (!empty($CFG->sessiontimeout)) {
@@ -184,7 +185,12 @@
                 }
             }
         }
+    } elseif(preg_match('/memcached/i', $session_class) === 1) {
+        throw new ErrorException('memcached shibboleth logout not implemented');
+    } else {
+        throw new ErrorException('cannot logout, unknown session class: ' . $session_class);
     }
+    
 
     // If now SoapFault was thrown the function will return OK as the SP assumes