Installing maps to computer

I have two Garmin Nuvi2595LMT, one for America and one for Europe. I have installed the current map for America on to my PC but I can't seem to do it for the Europe map.
I am using Garmin Express and the page comes up under "Map Options" and it shows the two buttons "Reinstall Map" and "Install to Computer" but the Install to computer button is inoperative.
Does anybody have any idea what is happening, both maps are lifetime updates etc. and as far as I can see there is no difference between the devices?