IDATs are the PNG format's compression tables, so this is something with that. Try another image format. Otherwise do the usuaul - check, whether you're not running out of disk space, check your color settings and so on.
Hmmm, my computer is having problems recently with not enough space on the main C Folder, but i don't know how to get rid of the (i think) temporary files.
I think that could be the main problem, thanks.
Hmm, it still gave me the same problem, i left 26 GB available in the C folder...Which kind of format would be nice to use as a Alpha image-sequence without taking too much disk space?
Sorry, but alpha-channeled images take a lot of storage space. You need more storage.
Which is probably a blessing in disguise -- it's not good practice to render to your system drive.