It works on a Dakota 20.
But it doesn't work on an Oregon 450 (latest firmware 3.80). I'm 100% the generated UNL file is correct.
I read somewhere about a new security method Garmin is using for new maps and that devices with recent firmwares are checking on this. Something about a certificate file (.gma I think) you also need for recent maps
Could this be the reason?

I used Jetmouse 1.5 with checksum check fix.