How to register a Student License?

Goodmorning.
I'm an Italian student. I followed the procedure to get a student license providing the SDK-ID of my school. Next I download the student edition and successfully installed and activate it on my laptop with the serial number sent to me by mail.
The problem is that when I try to register the student license on the my.solidworks.com  at the url:MySolidWorks - Official SOLIDWORKS Community , the web page prompt to me this error message: The serial number you have entered is not valid. Enter a new serial number or contact your professor.

How can I register my student license? I really want to learn from the my.solidworks.com contents

Thanks for your time!

SolidworksAdministration