Error Message "This is not a Test User account - Please create a new account in the Sandbox Environment" The above error appears to some people for different reasons: It might be after an IOS update to their iPad/iPhone/iPod. Other reasons would be an attempt to use your iTunes account information "Username & password" on other devices, for instance, if you enter your account information on someone else's iPhone which is already linked to their own user name & password, you'll face this problem later on when you try to access you account info for any reason update/download Apps, or whatsoever on your device. Some people do that to permit others download their own purchased books, Tv series, etc.. on other devices using iCloud to reinstall already purchased items!
The only way to solve this problem is to reset your device. First you have to enter iTunes ->Store, under Settings, click on your Apple ID and Sign Out. After signing out you should turn your device Off and then turn it On.
Then under Settings, enter the General Tap and select Reset.
You should only click on the first option "Reset All Settings" under Reset.
After reseting your iPhone/iPad/iPod you'll be asked to restore your data either by iCloud if you set one already, or by iTunes. If you select the option "Set to new device" you won't be able to synchronize your data! Make sure to transfer your contacts before reseting your device. other stuff like Photos, Notes, emails will be available and remain the same. There'll be some minor changes such as your phone sounds preference, and background wallpaper, will be set to the manufacturer settings, and your WiFi Networks passwords you'll need to insert them again. Do not forget to restore your device after the reset in order to be able to use it again!