It looks like you have a unique and strange problem. I use JCV files on my 1300 daily and it works fine (Always on SD card)
Try to use another SD CARD (Fat32 Format)
Try another Map / JCV combination (A small country just as a test)
Try to see if the JCV file registers in the Inventory Screen.
If it works in the unit it should also work on the SD card, make sure your path is correct (delete and re-create the folder).
Make sure that you don't have old JCV files somewhere.