I'm not sure you need to go messing around with sudo commands in Terminal to solve this.
I just had the same problem but cured it immediately by 'force quitting' the process in Activity monitor (ordinary Quit won't work).
1. Open Applications > Utilities > Activity Monitor.app
2. Ensure 'All Processes' is showing in the menu next to the Search/Filter bar
3. Type 'prl' in the filter bar (without the quote marks).
4. Choose the process in the window, and click 'Quit' in the taskbar.
5. Choose 'force quit' from the dialog box. You will need to enter an admin password.
(issue found with Parallels 6 on 10.6.8)
Last edited: Dec 23, 2011