I had a frustrating few minutes with mentalray today when i got this error message:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=13780301&linkID=12544120
Autodesk's pages are obviously their usual unhelpful selves and the only hint I came across was on a forum where Jeff Patton had suggested it was caused by an object scaled at 0%. On analysing my scene I found a sky portal object that was 100000x100000, probably due to snapping to scene extents by accident.
I hope this helps someone in the future who might trip over this post when they search for tech support on the same subject!
