GF1: "Insert SD card" error

I've had a few instances where my GF1 asks me to "Insert SD card", shortly after I removed it to transfer photos and insterted it back into the camera. Taking it out and inserting it again has always taken care of the problem. I imagine the problem could be with the card or with the camera, so I plan to try a different card first. But the problem occurs rarely enough that it may take a few weeks to find out whether changing the card actually does take care of the problem. Therefore I am curious to hear whether others have had a similar problem, and whether you found out that this indicated a camera malfunction.

Thanks in advance.

Drusus