Have just run into the same problem and fixed it very quickly by reinstalling AppleQmaster (on second level of FCP Studio Pro Install Disc 1 (the white disc).
Had not used Compressor for a while and am guessing a system overhaul a few weeks ago for an unrelated problem entailing complete removal of cache among other trashings, likely killed a few critical elements.
Compressor Repair 2.2.2 did highlight a qmaster daemon as missing; a handy clue.