I had a weird issue with my GPSMAP64... was using it on my boat, and it defaulted back to the base map. Checking available maps in settings, the topo map I have loaded on the microSD card didn't show up! I checked the microSD card on my laptop PC, and the card works and the map file is still there. It's like the GPS unit couldn't see the card. I installed the topo map on internal memory, as that would really suck having that happen on a moto trip. Anyone else experience similar?