Are you using the latest windows IE? If so, I've had the same issue, plus it won't work with my photobucket. I've had to add google to my system and use it when I upload. The IE also won't work with my bank account, I've had to use the google browser. I was on the phone with their IT desk and they were the ones who had me add google to get access. I'm not sure what they've screwed up.
Anyway, if you have IE try firefox or google or ? instead and see if the issue goes away. The only way I can get the IE to upload is to use the Go Advanced option and manage attachments. Then it will only do one at a time.