Wish I had your answer, because I have the same problem.
My Panasonic Lumix DMC-FZ30 has worked flawlessly, until today.
When I turned on the camera I got the same message: "Memory card error" "Please check the card"
Put the cardfthat was in the Lumix into another camera and it worked fine.
Put the card from another camera into the Lumix and got the above error message.
Any ideas?
Pete
August 2009