@skinniezinho
There are a few different methods to send an IMG file to a device which cannot be seen in Mass Storage Mode. The one i often used for such units as old GPSMAP and StreetPilots was utilising WebUpdater in command mode. See this thread: [Only registered and activated users can see links. ] and post there for more help if needed after reading though.

PS: Please don't quote a complete immediately preceding post, quote only relevant part/s if necessary.