I have a Nuvi 255W where I put, along with the main map (gmapprom) an aditional map named imgsupp.img and it would recognize both. I now bought a 3690T and copied the imgsupp.img file to the hidden .System folder, to the Garmin folder, to the root folder. But the unit will not see it. Only if on an external microSD. Is there a solution for having an additional map sitting on the main memory?