If you use the "Register Serial" button, as the name says, it asks for your SERIAL Number.
The one that begins with "STxxxxxx" it's your ORDER Number. Your Serial Number is NOT the same thing, it's called "Serial Number" on your purchase receipt.
You need to insert that one, and it must be correct
- Don't confuse the letter "O" with the number "0" ( most common error ) or vice-versa
- Be sure it's exactly identical
- Be sure you HAVE selected the correct product. Even if the serial is correct, if you select a different product, won't work.
If you are getting a different error, such an "activation error" or similar, then maybe there's a problem with your activation because you activated too many times. In this case, you should contact support via EMAIL, with your Order Number and we can check this.
But if you are getting a "25001 Serial not Found" error, it means you typed it wrong. There's no other solution other than typing it correctly.