Hi vbteam

Today has just appeared a problem with my forum, I have vBulletin 4.02 and when members click to read threads url of topic changes:

ie the url is correct request but after a few seconds of quiet with this code: 81 and that my site is out, or file not found 404

Can you help here who has experience with VB, where the jet and how to fix the problem.

Wishes for all.