Trouble with NDS Roms

So I have OpenEmu on Mac. It runs all other rome fine but when I download DS roms, it won't recognize them.

The core is installed and it still doesn't work

first edit instead of multiposting2nd use desmume for mac. here is its link
http://desmume.org/download/
this emulator is for nds ONLY and will work even on a mac.