I have a large file, about 3gb. When it Autosaves, it only gets about 2/3 of the way through the save, then errors out, leaving only a 3DM.TMP file. In that file, all geometry is there, just all of the vRay materials have been removed.
I CLEARALLMESHES and PURGE regulary before saving.
Never had an issue with large files like this one before, and other smaller files will Autosave no problem.