I have now fixed the bug but I still get "invalid location" when users browse any forums.
Nathan said
"It means that the person is either looking at forum.asp, topic.asp, or post.asp but the TOPIC_ID or FORUM_ID in their querystring does not exisit in the database. This will happen when - topics get moved - topics get deleted - users are playing around by changing the querystrings by hand"
And my question again :)
Are there any way to update the datebase so that the TOPIC_ID or FORUM_ID exist in the datebase. I find it strange that EVERY TOPIC_ID and FORUM_ID doesn't exist in the database....