I finally solved the problem thanks to another post on this forum (http://pro.autel.com:6688/autelsupport/TPMS/21669_2.jhtml).
Updating the device leaving the card inside leads to corrupt data. This should not be an option in the User Manual.
You have to:
- register the device
- take the card out of the device
- format the card (I did a full format, not a quick one)
- insert it into the PC
- start the Maxi PC Suite and log in and you can do the update on the card