This is seen on Windows 7 Clients, when logged onto a domain, after unlocking the machine. If you inspect the Event Log you will see Event ID 1015

"A critical system process, C:\Windows\system32\lsass.exe, failed with status code 255. The machine must now be restarted."

I put up with this for a while, and did a lot of Internet searching, some people suggested power settings and a host of other stuff, nothing worked, The final solution was found on "Technet", it involves changing the authentication method to the domain, and needs a registry change.

1. Start > In the Start Search box type type regedit > {enter}
2. Navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters
3. Create a New DWORD entry called DefaultEncryptionType
4. Set its value to (decimal) 23 or (Hexadecimal) 0x17
5. Reboot the machine.

Or If you are feeling lazy just download this, extract and run it, then click "Yes" to add it to the registry, and reboot.