I've heard of people being disappointed with results of uploading directly to YouTube from the Share workspace, but never of someone who couldn't log on at all.
It might be worth checking your logon and password.
As far as I could tell I was logged in. The failure notice comes at the end of the process. After rendering the video and then taking another it action, it says something like Uploading to youtube; when it gets to the end indicating 100% uploaded, then comes the failure message.
I will try again and double-check the sign in name and the password, but I don't think that is the problem.
Dude, if you are able to login to the share to youtube workflow then login can't be the problem. The problem might lie somewhere else.
Tech support ppl suggested me to cleanthe application data present at %appdata%\adobe\Online Services in case of problem with Share to youtube. You can try that too. Hope it works for you!!