We are running a mixed mode server group. Our primary domain controller is a Windows 2003 R2. We have a backup controller running Windows NT 4.0 SP6. On the NT machine we have SQL server running. User’s client machines are running XP. When a user logs on to the client machine and then runs an application it usually will run , but if you leave the machine for 40 or so minutes it then cannot access the NT machine? It asks for a user name and password. If you try the user name and password that you logged in with it gives an error. But if I put in an admin user name and password it connects up to the NT machine and can access the SQL DB. The clients are members of Domain Users and Pre-Windows 2000 Compatible Access. Also the NT folder is also set for Domain Users and Pre-Windows 2000 Compatible Access. Any idea why this is happening?

You have to manually sync the NT4 server. Go to Programs --> Administrative Tools --> Server Manager --> Computer --> Synchronize with Primary Domain Controller. Hope that helps.