When I got my K5 this 'Memory Card Error' happend three times, and always after I read out the card on the PC and popped quickly back the card. Then I noticed that when I put in the card and hold it down a little bit after I hear this 'klick', the Error do not happens. I know, this sounds odd ... but it works with my K5.
Thanks - I'll bear this in mind.
When I removed the SD Card, I held the camera with the opened card slot pointing down & taped the body of the K5 to see if anything came out - needless to say, there was nothing.