diff --git a/OpenSim/Addons/Groups/GroupsMessagingModule.cs b/OpenSim/Addons/Groups/GroupsMessagingModule.cs
index 92528a2dc9..bbb5e059d3 100644
--- a/OpenSim/Addons/Groups/GroupsMessagingModule.cs
+++ b/OpenSim/Addons/Groups/GroupsMessagingModule.cs
@@ -110,7 +110,15 @@ namespace OpenSim.Groups
             m_messageOnlineAgentsOnly = groupsConfig.GetBoolean("MessageOnlineUsersOnly", false);
 
             if (m_messageOnlineAgentsOnly)
+            {
                 m_usersOnlineCache = new ExpiringCache<UUID, PresenceInfo[]>();
+            }
+            else
+            {
+                m_log.Error("[Groups.Messaging]: GroupsMessagingModule V2 requires MessageOnlineUsersOnly = true");
+                m_groupMessagingEnabled = false;
+                return;
+            }
 
             m_debugEnabled = groupsConfig.GetBoolean("DebugEnabled", true);
 
@@ -260,7 +268,7 @@ namespace OpenSim.Groups
             // Sending to offline members is not an option.
             string[] t1 = groupMembers.ConvertAll<string>(gmd => gmd.AgentID.ToString()).ToArray();
 
-            // We cache in order not to overwhlem the presence service on large grids with many groups.  This does
+            // We cache in order not to overwhelm the presence service on large grids with many groups.  This does
             // mean that members coming online will not see all group members until after m_usersOnlineCacheExpirySeconds has elapsed.
             // (assuming this is the same across all grid simulators).
             if (!m_usersOnlineCache.TryGetValue(groupID, out onlineAgents))