I have a problem about registration in a test lab.

Server: ZCM10sp1 on Windows2003 R2 SP2 32bit
Clients: Windows XP sp2 only - 500 XP computers
Directory: eDirectory on some NetWare6.5 SP7 servers

XP computers are found without any problems and able to deploy ZCM agents; then XP computers are restarted according to the setting.
However, it shows "Registering" on most of XP computers on ZCC Deployment page but it never finish on most of them, while some are completed and registered without any problems. This registration process never finish even few hours later and those uncompleted XP computers are disappeared from ZC C if I run Discovery task again. Those computers cannot be found under Device on ZCC at all. But registered XP computers are sitting under workstation/Device as it should be.

If I do zac command to register on those failed computers manually one by one, it can be registered. But I do not want to do this manual work on hundreds on computers.

Does anyone has seen this issue?
If you know the solution, could you give me an advise, pls?