Hmmm. Tough one. Could be a resource problem when it gets to the post rendering stage. Try rendering the same file in using hardware mode. If it works, then try it again in MR but with default sttings. If that works, keep building up until it freezes. I know it sounds like a pain in the ass to do, but I'm pretty sure it's going to have something to do with the MR sttings.
Dave Baer
Professor of Digital Arts
Digital Media Arts College
Boca Raton, Florida
dbaer@dmac.edu