Hi
Have a look in the topic "Pre/Post processors".
In your case, I suppose there is a problem in the matisse launch script when he tried to capture the PID of Rubens process.
We tried to cover the most case but sometimes this step fail.
What is your PC configuration? Windows 7? 32 or 64 bits?
We already tried to give solution for such problems, but if you don't find any solution we only could help you with more information on your personal PC configuration
Regards
Christophe