Tablet PC with IMEI invalidity issue
The check digit of the IMEI is invalid, and usually the IMEI cannot be changed, or in come countries it can even be illegal.

For more information, see how the IMEI is formed and the check digit is calculated here, or see a related question here.

There are ways to recover an IMEI on Android devices, but for this you'd need a backup of some files from when the IMEI wasn't invalid.