My daughter recently returned to the UK after being in the US for nine months, and was unable to update her apps. She was getting a message saying something along the lines of her account wasn't valid in the UK store. When she checked her settings she definitely was registered with the UK store, and after much googling and stuff she ended up simply logging out of her account, then logging back in again and was then able to update everything as normal. Hope your solution is equally as simple.
