Ok I got another question: How can I stop the archive from giving output on "invalid thread" and "invalid forum" in the case that something was removed or moved?
Currently the path of this error messages is totally wrong although I want to simply get a 404 error if a forum or thread does not exist:
normal forum:
http://foobar.com/forum
archive:
http://foobar.com/forum/archive
wrong path:
http://foobar.com/forum/archive/forum