One of your problems may be the domain because you allow users to go to your site via
www.yoursite.com and just yoursite.com . You should either redirect that on your server (google it or search here - it's been covered many times before) or set the doamin to .yoursite.com . However, I dont' think that will fix this issue since I think it may have to do with the forums being in a separate directory. You should read that thread and see if that issue is covered in there.