Index: lams_common/conf/language/lams/ApplicationResources.properties
===================================================================
diff -u -red98b3790d94f07748756535ad1bebd3d97d01be -r423858087ec4d185fb33c3f569fc7ede1d43001a
--- lams_common/conf/language/lams/ApplicationResources.properties	(.../ApplicationResources.properties)	(revision ed98b3790d94f07748756535ad1bebd3d97d01be)
+++ lams_common/conf/language/lams/ApplicationResources.properties	(.../ApplicationResources.properties)	(revision 423858087ec4d185fb33c3f569fc7ede1d43001a)
@@ -56,7 +56,7 @@
 email.notifications.lesson = lesson
 email.notifications.tool = tool
 email.notifications.activity = activity
-error.requires.existing.grouping = Activity {0} requires existing grouping but no group for user {1} exists yet.
+error.requires.existing.grouping = In this activity you work in groups. Please visit the grouping activity first.
 validation.error.GroupingNotUsed = Grouping is not used in any of activities
 audit.change.mark = User {3} ({4})  Changed mark for user {0}. Old mark: {1}, new mark: {2}
 audit.started.editing.activity = Teacher {0} has started editing activity {1} in monitor
Index: lams_common/conf/language/lams/ApplicationResources_en_AU.properties
===================================================================
diff -u -red98b3790d94f07748756535ad1bebd3d97d01be -r423858087ec4d185fb33c3f569fc7ede1d43001a
--- lams_common/conf/language/lams/ApplicationResources_en_AU.properties	(.../ApplicationResources_en_AU.properties)	(revision ed98b3790d94f07748756535ad1bebd3d97d01be)
+++ lams_common/conf/language/lams/ApplicationResources_en_AU.properties	(.../ApplicationResources_en_AU.properties)	(revision 423858087ec4d185fb33c3f569fc7ede1d43001a)
@@ -56,7 +56,7 @@
 email.notifications.lesson = lesson
 email.notifications.tool = tool
 email.notifications.activity = activity
-error.requires.existing.grouping = Activity {0} requires existing grouping but no group for user {1} exists yet.
+error.requires.existing.grouping = In this activity you work in groups. Please visit the grouping activity first.
 validation.error.GroupingNotUsed = Grouping is not used in any of activities
 audit.change.mark = User {3} ({4})  Changed mark for user {0}. Old mark: {1}, new mark: {2}
 audit.started.editing.activity = Teacher {0} has started editing activity {1} in monitor
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/ToolActivity.java
===================================================================
diff -u -r1ee503e3d0e0228ea8a45025fddf15d9623c0377 -r423858087ec4d185fb33c3f569fc7ede1d43001a
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/ToolActivity.java	(.../ToolActivity.java)	(revision 1ee503e3d0e0228ea8a45025fddf15d9623c0377)
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/ToolActivity.java	(.../ToolActivity.java)	(revision 423858087ec4d185fb33c3f569fc7ede1d43001a)
@@ -75,17 +75,17 @@
     private Tool tool;
 
     @OneToMany(mappedBy = "toolActivity")
-    private Set<ToolSession> toolSessions = new HashSet<ToolSession>();
+    private Set<ToolSession> toolSessions = new HashSet<>();
 
     @OneToMany(mappedBy = "toolActivity")
-    private Set<CompetenceMapping> competenceMappings = new HashSet<CompetenceMapping>();
+    private Set<CompetenceMapping> competenceMappings = new HashSet<>();
 
     @OneToOne(fetch = FetchType.LAZY, mappedBy = "activity")
     @Cascade(org.hibernate.annotations.CascadeType.SAVE_UPDATE)
     private ActivityEvaluation evaluation;
 
     @OneToMany(mappedBy = "activity")
-    private Set<GradebookUserActivity> gradebookUserActivities = new HashSet<GradebookUserActivity>();
+    private Set<GradebookUserActivity> gradebookUserActivities = new HashSet<>();
 
     @OneToOne(fetch = FetchType.LAZY, mappedBy = "activity", cascade = CascadeType.ALL)
     private PedagogicalPlannerActivityMetadata plannerMetadata;
@@ -187,8 +187,9 @@
 
 		//check if activity requires existing grouping but no group for user exists yet
 		if (group == null || group.isNull()) {
-		    String errorMessage = messageService.getMessage("error.requires.existing.grouping",
-			    new Object[] { getActivityId(), learner.getUserId() });
+		    log.warn("Activity " + getActivityId() + " requires existing grouping but no group for user "
+			    + learner.getUserId() + " exists yet.");
+		    String errorMessage = messageService.getMessage("error.requires.existing.grouping");
 		    throw new RequiredGroupMissingException(errorMessage);
 		}
 
Index: lams_learning/src/java/org/lamsfoundation/lams/learning/service/LearnerService.java
===================================================================
diff -u -ra05bb8ff92c659cc340b037de664fd0d9b103c96 -r423858087ec4d185fb33c3f569fc7ede1d43001a
--- lams_learning/src/java/org/lamsfoundation/lams/learning/service/LearnerService.java	(.../LearnerService.java)	(revision a05bb8ff92c659cc340b037de664fd0d9b103c96)
+++ lams_learning/src/java/org/lamsfoundation/lams/learning/service/LearnerService.java	(.../LearnerService.java)	(revision 423858087ec4d185fb33c3f569fc7ede1d43001a)
@@ -333,7 +333,6 @@
 		lamsCoreToolService.createToolSession(learnerProgress.getUser(), (ToolActivity) activity, lesson);
 	    }
 	} catch (RequiredGroupMissingException e) {
-	    log.warn("error occurred in 'createToolSessionFor':" + e.getMessage());
 	    throw e;
 	} catch (ToolException e) {
 	    log.error("error occurred in 'createToolSessionFor':" + e.getMessage());