Last week Youtube made changes in log in system. If you are already logged in on Google site, your Youtube account will be automatically linked to you Google account.
I don't see why they are doing this, but was very frustrating for me.
I was having 2 Youtube accounts, one linked to my Google account, and another one not linked. When I was trying to log in with my "not linked" account (used daily) I was automatically logged on my "linked to Google" account for no reason (even if I wasn't logged on Google).
The solution for me was to delete my old account (linked to Google) and only after that I was able to log in with my daily Youtube account.
I don't know if you are in the same situation, but this might help. If I wasn't clear enough please ask me for details and I will answer as quick as I can.
