Hello,
Sounds like your doing remote OPC - it has plenty of permissions gotchas. This sounds like it could just be a subtle difference between DCOM settings under Windows 2000 vs XP, given that it works under all your XP machines. I found the following document regarding DCOM settings for Windows 2000:
DCOM (Distributed COM) for OPC
Just to cover our bases, here's a general document for troubleshooting error 1101 in conjunction with datasocket:
Getting Error 1101 When Using DataSocket with LabVIEW
Other reading of potential interest:
Remote OPC Server on Windows 95/98/Me
I hope this helps!
Best Regards,
JLS