BeatriceKarjalainen,
OK now we are getting somewhere... this combined with your message earlier about the directories has me thinking that you forum directory is not set correctly...
It looks to the "DOCUMENT_ROOT" of your website... which should be the root directory...
Based on you saying "(
www.parlplatsen.se/CMS/forum/) " I would think your forum directory should be "CMS/forum" without the quotes.
Greg