If none of the previous answers to this question have worked for you, you could try this, it worked for me:
1. Log in to forum.
2. Go to user control panel.
3. Click the "Profile" tab.
4. Click Account Settings.
5. Change Password to something else.
6. Once password is changed, sign out of forums.
7. Sign in again with your new password, and you should be able to access the rest of the site.
Hope this helps.
