If so, likely what happened to you is that there is a new version of Adobe Air that was just released. We've had a few people mention to us that it stopped working, and it has been because they did not have an up-to-date version of Air on their machine.
So if you are having issues where the uploader cancels after a few minutes of successful uploading try updating Adobe Air. Get the latest version here - http://get.adobe.com/air/
Please use this thread to report any issues!