Why can't I upload videos to YouTube on my iPhone?

I have an iPhone 4S with IOS6 and it won't let me upload videos to YouTube for some reason, when I tap the YouTube button it tells me to type in my username and password but then it tells me that one was incorrect time and time again, I've gone onto the app and signed out and back in so I know that they are correct. I have no idea how to resolve this problem

Try logging on from safari