Exchange Service Pack 3

I installed SP3 on our single Exchange 2000 server last week. After the installation our users who check there e-mail using VPN and then connecting to Outlook can not gain access to the server. A popup box keeps asking for their password. I have tried the following:
1) Reset their password on the DC and on their VPN connection.
2) Re-set up their VPN connection, tried different settings.

Has anyone else seem this problem with SP3?

Thanks,
Bill