You can confirm wheter or not Poser export is the problem by loading an unmodified exported body part as a morph target.

The try the same thing but import to and export from you modeller with no modification.

If neither of these causes an explosion, the problem is with what ever you modeller does when you modify the mesh and export.

To see exactly what is going wrong, work with simple (6 poly) cube, then you'll be able to post the mesh info so that we can diagnose the cause.