Mixbus could not start JACK

Hi, I just downloaded Mixbus, but the application doesn’t start. I always get a window saying:

"Mixbus couldn’t start Jack
There are several possible reasons:

  1. You requested audio parameters that are not supported
  2. JACK is running as another user.
    Please consider the possibilities, and perhaps try different parameters.
    You may need to force-quit a currently running instance of Jack."

I have no idea which parameters I should change.
I have OS X 10.7 and a Steinberg UR824 interface.

Thanks in advance for your help.

You are (probably) better off using the Mixbus support email that you received when you purchased Mixbus.

You might also want to read http://ardour.org/first_time_osx_native particularly the section on "It Doesn't Work!"