Question:

I am adding a new 2008 server to my 2003 forest as a primary domain controller I can’t run adprep /forestprep from the 2008 disk on the 2003 Domain Controller. But can’t add it without it I guess. Please Help!

Solution:

ADPREP /forestprep must be run on the Schema Master of a forest and under the credentials of someone in the Schema Admins and Enterprise Admins groups.

Is this true with the server and credentials you are using?