Solved: A Schema validation check failed.

[chicagotech]

Situation: when migrating SBS 2003 to Windows 2003 domain using dcpromo, you receive the following error:
The operation failed because: A Schema validation check failed.

The Active Directory Installation Wizard cannot continue because the forest is not prepared for installing Windows Server 2003. Use the Adprep.exe command-line tool to prepare both the forest and the domain. Fore more information about using Adprep.exe see Active Directory Help.

"The version of the Active Directory Schema of the source forest is not compatible with the version of the Active Directory on this computer."

Resolution: run ADPREP /domainprep on the SBS before runing dcpromo in the Windows server.