Cees,
I assume then that you have an exterior model, and an interior model ... 2 models.
1. Are the models the same size, located at exactly the same coordinates? Verify.
2. If so, then you may have a scaling issue with one of them (if you are developing in gmax).
Select each of your high order nodes (exterior, interior) and reset the scale for the pivots on them.
This ensures they will be exported at the same dimensions.
If you simply clone the exterior for the interior model, then simply reset the scale for teh exterior model before cloning.
3. Do you have crash points setup in the contact points section (type 2 points), if so, comment them out and try again.
If this is the cause, you may want to reestablish them by getting coordinates from your design program.