Hi papaoso. It is extremely difficult to troubleshoot something like this over the Internet, when we can not see what is actually being done and what has happened.
Please do not take this the wrong way, but in most cases, the problem is some sort of user error. Whether it is accidentally missing a step in the downloading and/or file setup on the USB, or when the USB has been inserted into the vehicle.
We can assume you had your vehicle running when you plugged the USB in, and kept your vehicle running? How long did you give the update to begin before giving up?
Are you downloading the SYNC3 update file on a PC or a Mac? If from a Mac, I would recommend trying to download from a PC (if you can), since we have seen a few cases of problems when downloading, unzipping etc., on a Mac
The only way to possibly help would be for you to type up every single step you took along the way (from file download to USB insertion), to see if you missed anything or not. It would be tedious for you. And even then, it would be difficult to assess the problem.
So my first recommendation would be to print up the full instructions, then download the file new and try again, following the steps exactly.
Forget about WiFi updates. Even with an exceptionally strong WiFi signal, they are iffy at best in SYNC 3.