Eu tive o mesmo problema (Linux guest no Windows host com o gerenciador de janelas do wmii). Esta hack do registro funciona perfeitamente.
Open up regedit.exe through the start menu search box, and then browse down to the following key, creating it if it doesn’t exist:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
On the right-hand side, create a new DWORD 32-bit value named DisableLockWorkstation and give it one of these values:
• 1 – Disable Lock Workstation
• 0 – Enable Lock WorkstationThe changes should be immediate, no need to restart anything.