Unless you registered the Mbox 2 hardware with a different email addresse, you only registered the Mbox2 Factory Software Bundle software portion. In order to receive the free update to Pro Tools LE 7 (which all Mbox 2 owners are eligible for), you need to register the actual Mbox 2 hardware.
See if you have another online registration card for that, and see the Registration Alert for Mbox 2 owners on the upper right side of the Customer Service section in the Support section:
www.digidesign.com/support/cs/
If you are still not able to register online, then you will need to contact Digidesign Customer Service Administration so they can take care of your registration manually, and then send you the email instructions for your free update to Pro Tools LE 7.
Contact information for Customer Service worldwide can be found here:
www.digidesign.com/contact