MAKING A PRIMARY SERVER

i hav made a domain with domain cotroller running window 2003 server. i want to install a central virus definition that sends update to client PC'c. my problem is that when i have installed an antivirus on the client systems running window XP or windows 2000 and them try to register them on server it gives the message "your server is either a unmanaged secondry server,make it managed server or primary server".
how can i troubleshoot the problem
do help me .thanx