It seems thad Domain name cannot be bigger than 15 characters (including dots).
I have 16 characters domain name and logging in to win2008 server it said incorrect username or password. And if I looked the username on screen there was one letter missing in the end of domain name.

As an example domain name is: ad.fourdomain.ee
After incorrect password message the username in win2008 server shows ad.forudomain.e\administrator. One "e" is missing.
Of cource I can change the username after that on server screen and then log in, but it takes time everytime.