not able to validate user in WIN2k domai

i have enabled ADS on win2k Server. this is first ever win2k Domain Controller.
after enabling ADS i created a new User called veronica. i got the following error message after creating a user.

” Windows cannot validate the uniqness of this proposed user name with global cataloge server because the server is not operational.

Windows will create this User account but the user can log in only after the user name is verified to be unique, for further assistance, contact your system administrator”

what is causing this & how do i enable global cataloge ??