This tip is from www.Digitalrebellion.com, courtesy of Jon Chapell
The "Unable to connect to background process" and "Unable to submit to queue" messages are common errors that unfortunately have many causes.
Before you do anything else, check that your version of Compressor is compatible with your operating system. Compressor 2.1 and 3.0 are compatible with OS X 10.5; Compressor 3.0, 3.5 and 4.0 are compatible with OS X 10.6; and Compressor 3.5 and 4 are compatible with OS X 10.7. If you have an incompatible earlier version, you will need to either upgrade Final Cut Studio or downgrade your operating system
Try the following steps:
1. In Compressor, go to Compressor > Reset Background Processing.
2. Run Compressor Repair.
3. Trash Compressor preferences (can also be done in Compressor Repair).
Do the following if nothing else works:
4. Disable your internet / network connections.
6. Perform a full erase and install of the operating system and reinstall from scratch.