This is a bit of an old issue, but it reared its head on one of our client servers that is not being managed in an ongoing basis by us.
This is what we found using the free utility called TreeSize Free:
Now, SEP on this server is not up to date yet, so we will temporarily delete the .TMP files until we can actually get in there and update SEP to the newest release.
MRU5 or later fixes this problem.
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book