It sounds like you're trying to open an unrecognised software on your sat nav.

It'll let you transfer it but you're software won't understand it's binary code and therefore won't be able to run it but will know it's there.

If it has an SD card slot, you can get a software that allows you to run any software on it. You can find them in places like Pirates Bay or even torrent it.

Failing that, you could always set your route up at every stop you make