Support reps, please check out the following thread on one of the licenced versions of UBB:
http://sysopt.earthweb.com/forum/Forum17/HTML/001740.html

This has been an ongoing problem. The administrator has tried all he can to resolve this issue, but can't find the bug. It is not a server issue, that has been determined. The issue resides withen the UBB, which has worked fine up until about 2 months ago, and the malfunctions have been increasing since. Please email me with your thoughts. [][email protected]<br[/] />
Thank you,

Micahel Morelli