Can't share song to YouTube

I've been trying to share my song to YouTube for weeks. I've managed to share an earlier version of it before, but every time I've tried since I've gotten an error message telling me to check my username and password - which I have, several times - as soon as the song finishes exporting and begins to upload. I've tried this with stable wi-fi and 3G connections. Is this a known issue? Is there a fix?