can't join windows 7 to winNT4 domain

have installed the Win7 RC. The Network Connection is working fine an via nslookup i can resolve my winNT 4 Domain controller and the domain name.

When I want to join the Domain I get the Message
"A Connection to the Domaincontroller (AC DC) for Domain "domain" could not be established"

The Domain name has less than 15 characters

Any ideas ?

Thank you

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