Ever get the dreaded "Can't Submit Batch: Unable to connect to background process" error when working with Final Cut Pro and Compressor? Well, it cropped up on my machine the other day and NOTHING would get it working again. Apple and all the FCP forums had several suggestions that had no effect whatsoever. I got it solved by going into the command line (Terminal) and typing:
sudo SystemStarter
This apparently relaunches all your Startup Items (again) and voila! -- Compressor is back in action, much to my relief. I posted this on several forums so hopefully it helps people fix their system.
UPDATE: Sometimes simply turning off your network will work as well and no command-line access necessary.