I will take a couple of guesses here.  The signature of the bike is on the USB stick correct?  What format is the USB stick in? It should be Fat32.  I know the bike is very particular on the type of USB drive.  You may want to try a 8 GB.  You should also receive a USB stick from Yamaha.  Mine was mailed to me.  I believe the activation code is good, it is the type or format of the USB drive that is causing the problem.