In our Open EdX course learners have to upload files to EdX in an ORA. The file extension is “.atlproj”. This filetype was also set in the ORA as an acceptable filetype. Nevertheless, EdX seems to change the file extension into “.zip”, so if the file submission is downloaded again it is downloaded with the “.zip” extension. The file itself is not corrupted and still has the “.atlproj” format. So changing the “.zip” extension back to “.atlproj” solves the problem. But this should not happen. I assume this is a bug in the OpenEdX software… which needs to be addressed.