logging into iTunes

I was logged into iTunes on my iPhone 4, I logged out, attempted to login under my other Apple ID, and it gave me an error message: "Cannot log into iTunes, an unknown error occured." Does anyone know if this is a common problem, and whether or not it is on my end (communication to apple) or on their end (communication from apple)?

Since then it will not allow me to login under either Apple ID. I have tried, while connected to a reliable wi-fi source, and while connected through cellular service. Still no luck. On to restart I guess.