Hi Allab7,

welcome to Questions & Answers..

Go to the My Sony page type in which model Tablet, etc you have & when you come to enter the serial number you should enter a 15 digit number..

To check you are entering the correct serial number power up your Tablet..

Then open Settings, touch About Tablet at the bottom of the list..

Under About Tablet  touch Status & you should see your Tablet's 15 digit serial number..

If you still have problems let us know..