If you've been having trouble joining domains when using Windows 7 beta or Windows Server 2008 R2 beta, this update is for you. Microsoft has detailed (KB article 961402) a problem with both beta operating systems trying to join domain names by using the System Properties user interface, the Netdom.exe command, an unattended setup, the Djoin.exe command, or when trying to use the Active Directory Installation Wizard (Dcpromo.exe) to install Active Directory Domain Services on a member server.

In any of these cases, you may get the following error message: "The attempt to join this computer to the .com domain failed. The parameter is incorrect."

Source:→ One Microsoft Way