From: Alan M Webb <alan_webb@us.ibm.com>

This fixes *another* sync error in a list/dictionary
  iterator. This time in WorldComm. I'm beginning to think
  something is going on...

OpenSim/Region/CoreModules/Scripting/WorldComm/WorldCommModule.cs

@@ -575,6 +575,8 @@ namespace OpenSim.Region.CoreModules.Scripting.WorldComm
         {
             List<Object> data = new List<Object>();
 
+            lock (m_listeners)
+            {
 				foreach (List<ListenerInfo> list in m_listeners.Values)
 				{
 					foreach (ListenerInfo l in list)
@@ -583,6 +585,7 @@ namespace OpenSim.Region.CoreModules.Scripting.WorldComm
 							data.AddRange(l.GetSerializationData());
 					}
 				}
+            }
             return (Object[])data.ToArray();
         }