I just bought a second PlayStation * controller and I would like to play Black ops * sp...

I just bought a second PlayStation * controller and I would like to play Black ops * split screen with a friend at my house but it's telling me that I need to sign into the PlayStation network to use the features I personally have subscribed for the PlayStation Network for a whole year and when I put my own credentials in under a different username meaning it's still my PlayStation I just recently added a you know when you're at the home screen or before the home screen you press the PS button and then it asks you who you want to log into I created another obviously mine the main user and then I created another user on the same PlayStation * but when I go to put my information in to sign into PlayStation Network it tells me that I cannot use that information because somebody else on this PlayStation * is already using that account but it's on the same PlayStation * why can I not use something that I paid * for a year on the same console same game same two controllers just split screen.