Is there anyone with the retail who are able to register there cd-key for the multiplayer?
Im not!

*edit* I have registreted it now but when im joining an empty server I get something like: Serial code is incorrect. You need a valid serial key to play multiplayer.

Is it because of demo-servers? Or what could be the problem.

wait until the release date.. the back end servers may not be up yet to recognise your keys..

wait until the release date.. the back end servers may not be up yet to recognise your keys..

Okey sounds reasonable