Users fail to logon at a server.

Logon to the server as an Administrator

Start User Manager for Domains (Start - Programs - Administrative Tools - User Manager for Domains)

Select "User Rights" from the "Policies" menu

From the drop down "Rights" list select "Log on locally"

Click Add, and select "Domain Users", click Add, then click OK

Close User Manager

Logout and a User will now be able to login