When I use more than 1 core, no files was written in output folder!
If I use 1 core, I can see the files.
I have 12 core MAC pro mid 2010 2.66 with Hyperthreading enabled, tot 24 processes
What plugins were used? Can you try without plugins?
Using a Mac pro on OSX? (I ask, because I use a Mac Pro also on Windows 7).