If it is an SDHC or SDXC card, particularly one of higher capacity it might have trouble reading it.
I had my best luck with smaller cards such as 2gb up to 8gb on the original controller.
The largest one I ever successfully used was 16gb.
Also, there may be some brands that won't work for one reason or another.
I have even had trouble on my computer reading some brands of cards.
My most reliable ones have been SanDisk or PNY, again the smaller capacity the better.
I think I had a Kodak or two that worked too.
You might try formatting the cards as FAT16, or just FAT if it will let you.
You might have to partition the card into smaller logical units to do that even if it means wasting some of its capacity.
I'll have to try doing that to see what happens.
If you scroll down a ways in this web page it explains why SD and SDHC cards have a known compatibility problem for some machines.
All in all you would be much better off using USB thumb drives if your controller will allow it (I don't know what you are running).
I have a Smoothie board setup with a color touch screen on my FT5 and thumb drives are all I am using lately.