I assume you are using SD cards purchased from a know good source.
Ebay contains lots of counterfeit memory cards.

Something to try:
If you have a card reader/writer on your computer:
Put the SD card in the card reader and delete every file and folder you find on the card.
Then put the SD card in your camera and use the Camera's Format command to format the card.

That usually works for troublesome cards.

If that does not work, I suggest you go to our Samsung Forum and post your question there.
That forum has moderators that work for Samsung.

Here is a link;
http://forums.cnet.com/5204-13973_102-0.html?forumID=146

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