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

The image render module is returning everything twice. Once with
  data, once with null. This change adds a return to stop this
  behavior. This was not apparent until I added a message to the
  catching routine which issued a warning message when no data was
  returned.

OpenSim/Region/CoreModules/Scripting/LoadImageURL/LoadImageURLModule.cs

@@ -211,6 +211,7 @@ namespace OpenSim.Region.CoreModules.Scripting.LoadImageURL
                     }
 
                     m_textureManager.ReturnData(state.RequestID, imageJ2000);
+                    return;
                 }
             }
             catch (WebException)