I was ready to upload a Movie Maker video to Youtube. I typed in the correct username + password, only to receive the error: "Invalid Username or Password. Please try again."

I typed in my Google+ name

My email

My old youtube name (before it changed to my Google+ name)

I checked to see if caps was off

Carefully typed in the password 

Changed my password THREE TIMES 

Still nothing. What's going on? This is a real pain.