K-3 Card not formatted error

During a shoot today the error message came up on the screen of the K-3 Card Not Formatted 1. I assume the 1 was a reference to the card in use. Switched the camera off then on again and it has worked as normal, all the previous images were on the card, a Lexar 16GB 400x, and functioned ok for the rest of the shoot, taking normal and long exposures. Any suggestions as to what has caused this, anyone else experienced this. The sdhc is a fairly new one and was formatted in camera the previous day.
Have only recently acquired this camera, it was bought off a forum member and had very low shutter count of just under 1800.

Thanks in advance for any help or advice

Thanks Bill. I have ver 1.21 it was the first thing I did after getting the camera. I won't be using that card again, as you say probably have been lucky. At least with the K-3 there are two cards so had a "spare" Will look for another couple of cards. This is the first problem I've had with cards, used Duracel and other Lexar but it is a bit off putting when something like that happens. Still as long as it's the card and not the camera

Thanks All for the feedback. I don't think I'd trust that card again and will look for other marques as suggested