Index: lams_monitoring/src/java/org/lamsfoundation/lams/monitoring/service/MonitoringService.java
===================================================================
diff -u -rf653fb3f6e855e0c8190b0911df51673814b65a9 -r97e51b5fbdba25efaa0760489aca191ba14b14d7
--- lams_monitoring/src/java/org/lamsfoundation/lams/monitoring/service/MonitoringService.java	(.../MonitoringService.java)	(revision f653fb3f6e855e0c8190b0911df51673814b65a9)
+++ lams_monitoring/src/java/org/lamsfoundation/lams/monitoring/service/MonitoringService.java	(.../MonitoringService.java)	(revision 97e51b5fbdba25efaa0760489aca191ba14b14d7)
@@ -1619,8 +1619,10 @@
 	learnerProgressDAO.updateLearnerProgress(learnerProgress);
 
 	User learner = learnerProgress.getUser();
-	for (Activity groupingActivity : groupings) {
-	    Grouping grouping = ((GroupingActivity) groupingActivity).getCreateGrouping();
+	for (Activity activity : groupings) {
+	    // fetch real object, otherwise there is a cast error
+	    GroupingActivity groupingActivity = (GroupingActivity) getActivityById(activity.getActivityId());
+	    Grouping grouping = groupingActivity.getCreateGrouping();
 	    if (grouping.doesLearnerExist(learner)) {
 		// cancel existing grouping, so the learner has a chance to be grouped again
 		Group group = grouping.getGroupBy(learner);