I have a MacBook Air and I have done my assignments a few times and saved them different ways but they always submit blank. I am using google crome.
I use a macbook air as well . Have you made sure that your files that your are saving are displaying the type of file such as .docx or .mp3 or .pdf. Sometimes when transfer occurs between mac and PC or especially when you load into a shell system, if they are not speaking the same language, they are translation errors. You might want to try more than one browser. I came upon your post using Safari (which by you can run as different browsers on the Developer tab). I use 3 browsers in rotation of success. Safari, Firefox, and Chrome. That being said - see if your files are displaying the extension when they upload.
Here is a helpful article
This may be 100% unrelated but there could be two things going on. #1 I know that that uploader does require an up to date version of Flash (as far as I know) and an old/out of date one can make these types of issues happen. I've also had issues with the extension file name being odd. For example if you have a .pdf saved as filename.PDF, that capital PDF extension could be breaking the previewer.
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