* Added a lock to the user profile cache to prevent simultaneous duplicate additions to the database. (Attempting to fix bug reported by nebadon)

OpenSim/Framework/Communications/Cache/UserProfileCache.cs

@@ -58,6 +58,9 @@ namespace OpenSim.Framework.Communications.Caches
         /// </summary>
         /// <param name="userID"></param>
         public void AddNewUser(LLUUID userID)
+        {
+            // Potential fix - Multithreading issue.
+            lock (UserProfiles)
             {
                 if (!this.UserProfiles.ContainsKey(userID))
                 {
@@ -74,6 +77,7 @@ namespace OpenSim.Framework.Communications.Caches
                     }
                 }
             }
+        }
 
         /// <summary>
         /// A new user has moved into a region in this instance