If restating a region, clean up the physics scene after the main scene has been closed not before.

If this is done before then on ODE agent update calls still incoming can fail as they try to use a raycastmanager that has been disposed.
Bullet plugin does nothing on Dispose()
However, I wouldn't be at all surprised if individual region restarting was buggy in lots of other areas.

OpenSim/Region/Framework/Scenes/Scene.cs

@@ -1032,13 +1032,13 @@ namespace OpenSim.Region.Framework.Scenes
                 }
             }
 
+            m_log.Error("[REGION]: Closing");
+            Close();
+
             if (PhysicsScene != null)
             {
                 PhysicsScene.Dispose();
-            }
-
-            m_log.Error("[REGION]: Closing");
-            Close();
+            }            
 
             m_log.Error("[REGION]: Firing Region Restart Message");