Have you changed your password at any point? If so, did you do it through your Profile, or through 'Forgotten Password' on the Home Page?
If you can only login to the forums, this is the only thing I can think of at the moment. A solution, and a possible way to resolve this, is that you change your password through the 'Forgotten Password' link and do that anyway, and see if your issues are resolved after making this change. After the password change has been made through that method, you should be able to login through the Login page, User Panel and In-game.
Note for future reference: When you change your password through your profile on the forum, that only changes your forum password. It does not sync in-game. However, when you change your password by resetting it through the 'Forgotten Password' link on the Home Page, your password will be reset both on the forum and in-game.
Hillo, Zarum!
I also want to throw in, if you've changed your password at any point that could be the culprit as Bawfle stated. That can mess your account up, it did for me (actually the exact same thing) and I just emailed the password change email I forget what it was but a link there helped you changed it and then it worked for me. ^-^" Hope this helps!
Let us know if anything works!