We are not sure what causes this message. Most likely, it is just a bug. Here are some steps you can take which will likely resolve it:
- Go into Settings > General > Reset > Reset Network Settings. This will not delete any apps or data and it will not need to be re-enrolled, but it will reboot the iPad.
- After it reboots, go into Settings > Cellular Data and tap "Manage Sprint Account". This should show the Sprint logo and then after about 45 seconds it should show an OK button. It might also give an error message such as "Unable to Activate Carrier Network" or "Connection Failed". If you get an error, you need to connect to a Wi-Fi network and go back into Cellular Data and tap "Manage Sprint Account" again. As long as you have Wi-Fi Internet access, you should not get the error message from Sprint.