Also try formatting (both) cards using different filesystems. FAT seems to be a bit of a standard, but some basic SD readers may not be able to read something more proprietary like Mac OS (Extended, Journaled, or both). See if you can get a info sheet on the SD panel and see if it lists compatibility info.
What size was the card you tried? Some larger cards may not be recognized either. Try something under 2gb.
Master Tinkerer