One of the first places to start is to search the event logs on the local computer or a domain controller for account lockout problems.
Below is a list of common problems that can cause an account to get locked out:
- Is the account logged onto more than one machine?
- Check the following area for processes that could be running under invalid cached credentials:
- Mapped drives
- Task Scheduler tasks
- System services
- Proxy or firewall authentication
- Run a malware scan on the local computer.
Note: This problems can also be caused by badly configured security policies on a large network.Microsoft also offers the Account Lockout and Management Tools that can be used to help troubleshoot these types of problems. Check out a tool called EVENTCOMBMT.EXE.