Anyways, I found the problem, those cookies were probably unfunctioning, so after a quick deletion of all www.artsoft.org cookies, it now works again

Could this be a PHPBB-bug?
It has happened many times, especially with this forum, that the forum forgot me so I had to log in again - even though I save cookies on my computer...
So now you know what to do if the forum goes mad at you, delete your cookies and try again!