Site is logging me out
I also spent time with my host server this evening and created an Admin Account for the tech...the tech was able to upload a file!! but then after our session, using the same log in details i had just created for the tech, i was not able to upload a file. the site kicks me off again still.
I think she ended up using Firefox which seemed ok, but very rarely an issue like this does seem to crop up.
Are your browser cookie settings all enabled?
I'm not a big fan of Apple. I would try to see of everything works on a Windows computer with a proper browser like Chrome or Firefox. It could be Apple related. If that is the case you would probably have to submit a bug in the big tracker.