Server 2003 into a Server 2000 Domain

I’m trying to integrater Server 2003 into my server 2003 domain. I’ve promoted the 2003 box to a DC. I’ve ran adprep /forestprep – adprep /domainprep. I’ve also used the ntdsutil to seize all settings (?) Now if i try and add users to the server 2003 box it won’t let the user login & if i add a user to the 2000 box it says it cannot validate uniqueness with global catalog server

I am not using Exchange on the server 2000 box.