I can't sign in to Youtube on my iPod

I used to be able to access my youtube account fine from my iPod touch, 1st generation, but suddenly I change my youtube username and it doesn't work. I've restarted the youtube app, but that doesn't seem to do anything. It only says 'Authentication Failed, Sorry, your login was incorrect,' even though before I had no problem logging in. If it helps to find a solution, my youtube account is Wildfiery88. I hope someone can help, and if you have an answer, please do share it with me! Thanks!