I’ve just had the same problem and finally after much searching online with very little definite info I did a couple of things.
Firstly I trashed the preferences for Compressor, Batch monitor and another one with compressor in the name. Then I restarted the computer resetting the pram (as soon as you push the on button press “apple, option, p, r”.) Allow the computer start up to sound 3 times.
Then I went back to Compressor history and cancelled the jobs that I had inadvertantly lined up and they actually cancelled.
Pay no attention to what is happening in the batch monitor as it will follow suit when the history side is sorted.
I hope this helps anyone including yourself.
You can let me know if this works for you.
Cheers
Lisa
Mac 10.5.3 Dual 2ghz proc. 1gb ram.