Hi William,
Are you using Ross turnkey hardware, or custom built hardware?
Can you confirm which version of XPression and Nvidia board and driver you have installed?
I've seen issues in Bumpmapping using NVidia driver version 320.49 and newer. This should not longer be an issue in XPression versions 5.4 2616 and newer.
Depending on which NVidia board you have, one option may be to roll back to NVidia driver version 314 or so.
Brian
#XPression