* Nasty hack to reduce the incidence of spurious exceptions where a user deletes a newly rezzed object before the persistence thread gets to it from its queue.

* This should greatly reduce but not eliminate the problem - elimination probably requires a redesign of the prim persistence processes

OpenSim/Region/Environment/Scenes/InnerScene.cs

@@ -236,7 +236,15 @@ namespace OpenSim.Region.Environment.Scenes
                     // Don't abort the whole update if one entity happens to give us an exception.
                     try
                     {
-                        m_updateList[i].Update();
+                        // A null name signals that this group was deleted before the scheduled update
+                        // FIXME: This is merely a temporary measure to reduce the incidence of failure, when
+                        // an object has been deleted from a scene before update was processed.
+                        // A more fundamental overhaul of the update mechanism is required to eliminate all
+                        // the race conditions.
+                        if (entity.Name != null)
+                        {
+                            m_updateList[i].Update();
+                        }
                     }
                     catch (Exception e)
                     {

OpenSim/Region/Environment/Scenes/Scene.cs

@@ -2676,7 +2676,7 @@ namespace OpenSim.Region.Environment.Scenes
         /// </summary>
         /// <param name="group"></param>
         public void DeleteSceneObjectGroup(SceneObjectGroup group)
-        {
+        {           
             SceneObjectPart rootPart = (group).GetChildPart(group.UUID);
             if (rootPart.PhysActor != null)
             {
@@ -2693,6 +2693,14 @@ namespace OpenSim.Region.Environment.Scenes
                 m_innerScene.RemoveAPrimCount();
             }
             group.DeleteParts();
+            
+            // In case anybody else retains a reference to this group, signal deletion by changing the name
+            // to null.  We can't zero out the UUID because this is taken from the root part, which has already
+            // been removed.
+            // FIXME: This is a really poor temporary solution, since it still leaves plenty of scope for race
+            // conditions where a user deletes an entity while it is being stored.  Really, the update
+            // code needs a redesign.
+            group.Name = null;          
         }        
 
         /// <summary>

OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs

@@ -128,7 +128,8 @@ namespace OpenSim.Region.Environment.Scenes
             {
                 if( m_rootPart == null )
                 {
-                    throw new NullReferenceException(string.Format("Object {0} has no root part.", m_uuid));
+                    throw new NullReferenceException(
+                        string.Format("[SCENE OBJECT GROUP]: Object {0} has no root part.", m_uuid));
                 }
 
                 return m_rootPart.GroupPosition;
@@ -164,7 +165,7 @@ namespace OpenSim.Region.Environment.Scenes
             get {
                 if (m_rootPart == null)
                 {
-                    m_log.Error("[PRIMGROUP]: Unable to find the rootpart for a LocalId Request!");
+                    m_log.Error("[SCENE OBJECT GROUP]: Unable to find the rootpart for a LocalId Request!");
                     return 0;
                 }
  
@@ -1948,7 +1949,7 @@ namespace OpenSim.Region.Environment.Scenes
         /// Completely delete this group and tell all the scene presences about that deletion.
         /// </summary>
         public void DeleteGroup()
-        {
+        {            
             DetachFromBackup(this);
             
             lock (m_parts)