Index: grouplib.php
===================================================================
RCS file: /cvsroot/moodle/moodle/lib/grouplib.php,v
retrieving revision 1.31
diff -U 3 -r1.31 grouplib.php
--- grouplib.php	15 May 2008 21:40:01 -0000	1.31
+++ grouplib.php	19 Jul 2008 07:23:38 -0000
@@ -544,7 +544,7 @@
     }
 
     // init activegroup array
-    if (!array_key_exists('activegroup', $SESSION)) {
+    if (!isset($SESSION->activegroup)) {
         $SESSION->activegroup = array();
     }
     if (!array_key_exists($course->id, $SESSION->activegroup)) {