Thank you both Nlin and M.Igarashi for a patch that:

Attached patch protects against a NullReferenceException 
in SceneObjectGroup.stopMoveToTarget (used by LSL function 
llStopMoveToTarget). Thanks to M. Igarashi.

1 files changed, 4 insertions, 1 deletions

diff --git a/OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs b/OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs
index dd7628d..02098b7 100644
--- a/OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs
+++ b/OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs
@@ -1458,7 +1458,10 @@ namespace OpenSim.Region.Environment.Scenes
             SceneObjectPart rootpart = m_rootPart;
             if (rootpart != null)
             {
-                rootpart.PhysActor.PIDActive = false;
+                if (rootpart.PhysActor != null)
+                {
+                    rootpart.PhysActor.PIDActive = false;
+                }
             }
         }