Are you asking about http://code.google.com/p/jforum2/ or about http://jforum.net/ ? They have different code bases. Furthermore, it's impossible to tell what might be going on without knowing what code is being executed when this problem occurs. So: what are you trying to do, and what output do you see in the various log files? There should be more information in one of them.
I wasn't selected to go to mars. This tiny ad got in ahead of me: