Support › Meta Box Group › file_upload & post edit
It seems with file_upload type there is an error when the post is edited (not when he's new).
It's not possible to add a new file.
please see http://imgur.com/Uit223t
Let me check it again with the developer for file_upload. It's a revamped version of plupload_image (but for file) and now is very similar to file_advanced. I will get back to you soon.