When simultaneously requested images to be generated, one runs in the attached error. Some images can get generated, some not.
You can see in the images repository, that only the ones showing on the page are really generated.
The others requested are not generated in the imaging repo.

Sample URLs:
<img border="0" src="/.imaging/gen-size-m/website/home/works/work1002/images/0.jpg"/>
<img border="0" src="/.imaging/gen-size-m/website/home/works/work1012/images/0.jpg"/>
... and so on. Its taking one binary out of one page (workXXXX in the 'images' collection, first child '0').

The configuration of the generator is attached as a print screen.