A lot of folks use Apple's Compressor to create podcast video files. That is when its running. I use Compressor all the time and think its a great application that harnesses the power of Apple hardware and software... but it can be a bit buggy.
Apple has posted a useful article on what to do when Compressor isn't starting up properly or performing normally.They offer basic troubleshooting steps to remedy the situation. This is the right place to start if you are attempting to to submit a batch and you see the following message:
Unable to submit to queue. Please restart your computer or verify your Compressor installation is correct.
Check out the whole article here.