First time had any difficulties uploading to YouTube. It gets to the "Transferring File" stage and nothing happens - no error message. It's ony a 12 minute video - the only thing different to previous uploads is I'm uploading it as "Private" ?
Direct transfers to YouTube have always been intermittent. Sometimes it works and other times it doesn't. My guess is that the companies as big as YouTube (Google) and Adobe don't share the changes to their protocols well which get in the way of the automated upload.
The solution is to output a good quality video to your computer, review it and then use the YouTube uploader. Total time will be about the same. It can be less if you find things you want to change during the local review.