I ran into this today while trying to get some renders out. I checked around the office, and some of the other guys have been running into the same problems.
Apparently, it has to do with texture sizes and formats. They told me it started when we upgraded to v5. The workaround so far has been to change all file textures to .iff and to keep tabs on their size.
I haven't had enough experience with the problem yet to add anything further.