ConvexHull for SceneNode with ManualObject

Hi,

I try to use MogreNewt for collision detection.
When I create a ConvexHull I get an exeption.
colHull = new MogreNewt.CollisionPrimitives.ConvexHull(nWorld, targetNode);
// OGRE EXCEPTION(2:InvalidParametersException):
// Object index out of bounds. in SceneNode::getAttachedObject
// at ..\src\OgreSceneNode.cpp (line 159)
It seems so, that there is a problem, when there is a MovableObject attached to the SceneNode instead of a Mesh.
Is it right?
A ChildSceneNode is not attached. (I read this throws the same exception)

By the way - is there a performance difference (speed / vertex buffer use), if I convert a MovableObject to a Mesh?
(I have many of it in my scene, wich are permanent turning and moving)