I am aware that this is an old thread.
I have just been having this problem too, for the first time, and it took me ages how to figure out how to format the card in camera. I formatted the card on the computer, but this did not work when the card was inserted back into the camera.
So, this is what I did and, at this stage, it seems to work:
1) Insert the 'offending' card.
2) Set camera to 'Cust' on the top dial. This will bring up the 'Custom' menu. (No idea whether the camera has to be set to 'Cust', I just did because the needed menu came up).
3) Hit the left cursor on the menu dial on the back of the camera and then scroll down to the wrench.
4) Hit the cursor on the right
5) Use the down scroll button to go through all the numbers at the top until you get to '5'.
6) 'Format' will be highlighted.
7) Hit the right cursor and the menu 'Format' menu will come up asking whether you want to erase all data from the memory card.
Hitting 'Yes' will clear ALL data. So, before you hit 'yes', make sure you have all your pictures transferred to your computer. If you couldn't transfer the pictures, may be then you just have to forget about them. If you can't transfer the files, maybe it would work if you copy and paste them to your computer and format the card after.