No access to memory card on the Nintendo DSi?

I have a problem with my Nintendo dsi. I have had it for a long time and earlier I have always had my games on a memory card. At some point I think I did a system update or so and since then I can't access my memory card anymore. Whenever I want to open it on my Nintendo, it says, "An error has occurred. Press and hold the power button to turn off the system. Please refer to the Nintendo DSi manual for more information."

What should I do? Did any of you ever have the same problem?

I once read somewhere that you should never download an update for your console if you use such cards, because the console is then no longer able to "read" these cards.