Using VMLoginInGuest() when user is on a domain

I'm having a bit of a problem.  I have a Perl script using the VIX API to control VM's on VMware Server 1.0, and I'm having trouble correctly executing VMLoginInGuest.  Previously the script I created worked fine, but then I moved the Windows VM's to a domain hosted through Windows 2003 Server, and that's where the problems began.  I'm trying to provide the user/pass for that domain user, and I'm getting authentication errors (VIX_E_CANNOT_AUTHENTICATE_WITH_GUEST) from VMLoginInGuest.

Any idea on what I can do? My script is trying to copy over and execute some programs as the domain user, and I can't execute those commands unless I'm logged in.