Was BackupExec installed on the W2KPro machine before the W2KServer backup was retired?
if so, open up your favorite registry editor and drill down to HKLM\Software\Veritas\BackupExec and do a search for the Old Server Name (don't remember the Key off the top of my head, sorry). Delete from there, install the Remote Agent in the Server and you should be good to go
Oh Yeah - Remember that editing the Registry can be dangerous, be careful