Index: /branches/autoquest-core-tasktrees-alignment/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskBuilder.java
===================================================================
--- /branches/autoquest-core-tasktrees-alignment/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskBuilder.java	(revision 1738)
+++ /branches/autoquest-core-tasktrees-alignment/src/main/java/de/ugoe/cs/autoquest/tasktrees/treeimpl/TaskBuilder.java	(revision 1739)
@@ -33,5 +33,4 @@
 import de.ugoe.cs.autoquest.tasktrees.treeifc.IUserSession;
 
-// TODO: Auto-generated Javadoc
 /**
  * <p>
@@ -252,8 +251,7 @@
 						.equals(child.getTask())))) {
 			throw new IllegalArgumentException(
-					"the task of the child instance to be added does not belong to the children "
-							+ "of the task of the parent instance");
-		}
-
+					"the task of the child instance (" + child.getTask() + ") to be added does not belong to the children "
+							+ "of the task of the parent instance (" + parentTask.getChildren().get(seqInstance.size()) + ")");
+		}
 		seqInstance.addChild(child);
 	}