Here is another user with identical probem as mine, and why this happen
Quote:Awhile ago, google was spamming me to signup a google+ youtube account everytime I posted a comment. I finally caved in a created one, because it was getting annoying. It then split my account into two, one with all my history and subscriptions that I renamed, and the other a blank with my email address as the username.
This creates all sorts of problems when logging in. When I sign in with the xbmc youtube addon it logs in to the blank account, although in the youtube settings I have it set to default to the main one when logging in. I tried logging in with the google+ email directly associated with the main account, but I always get a Login Failed error.