can't log-in Win2K client?

[andrew kagan]

I just installed Client 5.1 on a Win2K box for the first time.   The box shows up in the network clients list, but when I try to log in, it prompts for a security code, and then gives me an error 507.   I know the security code is correct...before I uninstall and reinstall, is there anything I need to know about Win2K installation?