This problem is seriously pissing me off. The Iphone that I own previously belonged to my mom, but she didn't delete the stuff that she had on it. This wasn't a problem at first, until something stupid happened. Out of nowhere, a fucking window that asks me to sign into iCloud started to popup constantly. Every time I exited the window, it would pop back up every 2 seconds. It's really starting to get under my skin. How can I stop this shit without delete anything, because I have some contacts there that I need to have.
Try logging out of iCloud in the Accounts section in the Settings App. I had a similar issue. I logged out and logged back in. I had to do this because I had changed my iCloud credentials.