Working fine for me, so I have to ask the obvious questions first:
Are you uploading a ZIP file or a 7Z file? 7Z files are not allowed. The easiest way to do ZIP files is through Windows Explorer: Highlight all the files you want to zip, then right-click and select "Add to 'generatedarchivenamehere'.zip" or "Add to archive..." if you want a different name. DON'T CHANGE OR ADD A DIFFERENT EXTENSION NAME! Leave it at .zip or delete it if you want.
Are you uploading file formats accepted by IF? Only these formats are allows: JPG, GIF, BMP, PNG, ZIP.
If you can post a screenshot(s) that would also help.