+1 to what Rickie said.
The *.GPX file format is more of a universal file format. It is what our HumminbirdPC program uses and many other programs can use as well. the unit uses our own *.HWR file format. By using the HumminbirdPC program it will convert the file to the *.HWR file format and build the correct file structure on the SD memory card.
Greg...thanks for confirming that for me and DG00.....
Sometimes my memory gets a little cloudy and I post in hopes that someone will confirm.....