The Game Creator screwed up patch 5.2 when they added a new .x parser. Uninstall and update to patch 5.1. The problems have been identified and fixed in-house. But, they have not fixed the patch or posted a warning. Stay at 5.1 and wait until 6 and you should be fine. Patch 5.2 added jack in the way of functionality for most users since it was to mainly support a Caligari product.
If you do not want to re-install DBP, try trianglulating your models since it is quad (or higher) polys that the new parser can not handle.
--
TAZ