That's because you inserted the wrong activation key or ( a common mistake ), selected the wrong product to activate.
- If you want to activate GSX, you should selected GSX from the Addon Manager list, press the "Register Serial" button and use the GSX Activation key
- If you want to activate GSX Level 2, you should selected GSX Level 2 from the Addon Manager list, press the "Register Serial" button and use the GSX Level 2 Activation key