Crash after specific number of trials

Hello everybody,

I set up an experiment with opensesame and everything works fine with one exception:
After 70 runs, I suddenly get the following error "'c:\users\username\appdata\local\temp\tmpkznxjo.opensesame_pool\7_pink.jpg' is not a supported image format"

The experimental structure looks like this:
Out of 12 images, 5 are randomly picked. This set of 5 pictures is presented 24 times (loop).
If I loop only 2 times through the set, everything works just fine. But 24 loops seem to be a problem.
I get the above mentioned error after the presentation of about 70 images. The image name changes (it's not always "7_pink.jpg"). I already changed the backend, but this doesn't help (I work with the legacy-backend). And I tried to disenable garbage-collection in the general settings and to collect garbage manually (in a script with "import gc", "collect.gc()") at the end of every loop. Neither of this works.

Any help would be highly appreciated!

Thank you very much in advance!

Best, Lea