Outlook wont connect to Exchange

I have a network of PCs with outlook 2000 running on an Exchange 2000 Server, on SBS2000 system.
One PC had some spyware installed that has since been removed, but now outlook let that user connect to the exchange server.
It will communicate with the exchange server, but wont accept the users password. He can connect with the same username and password from other machines, but not his own.
I have reinstalled outlook, and applied updates to outlook and win2k.
Any ideas?