[Serusers] Can't find last registered users when proxy and registrar is distributed at two machines.

Hi, All: My SER is located on two different PC. One is Registrar and RADIUS, DNS server , MySQL. the other is Proxy server only. All started successfully and run well. After a while, I registered the fourth user. Now I can call the previously registered three users with latest registered user.But failed the other direction. When I call the newly registered user with first registered user. the SER report "404 Not Found". What happens to the Registrar and Usrloc modules? I guess the problem lies in that two modules. Am I right?? Thanks for your instructions and help! Best Regards. Sun Zongjun.