This error message can be attributed with an issue with the Apple ID. To make sure everything is entered correctly - please follow the steps below:
- Go to "Settings" on your Device (not through the App)
- Scroll down to "iTunes & App Stores" on the left hand side
- Then click on "Apple ID" on the top
- A pop up window will appear with four different options; "Sign out".
- Turn off and restart your device.
- Then, go back into "Settings" and re-enter your Apple ID and password.
- After you've done this, log in to the App.
Also please ensure your iOS software is up to date:
- Go to "Settings" on your Device
- Tap on "General"
- Tap on "Software Update"
For more information on how to update your device, visit the Apple Support page.
If you continue to receive the error message even after performing the steps above, please visit Apple Support Communities or contact Apple directly for further assistance: http://www.apple.com/support/