Some vertex's were the problem.

//phcon_setmotor(oid,vector(kreuzespeed,800000,0),nullvector,nullvector);

I didnt work with ODE, but my Newton experiense told me that you may try to play with 8000000

try make kkreuz1 and pplatte add to one group, if they aren't

Fixed, the problem were a vertex or 4 somewhere around the kkreuze!