Error 2

I was getting error 2 on a lease class 10 card. 16gb 30mb/s. Never when shooting. I noticed that my continuous count on my camera was at zero. I keep it continuous just to give me an idea what my actuations are and I always use the same card. I put it in after removing photos on my pc and for error 2. I formatted it in the camera and it seemed to work. Then I went back to the pc to change the image file number to let's say img_10000 to pick up where it left off. Put it in showed fine. Took it out to test to see if images were readable put in error 2. Put another card in and left it over night and it's fine. All of my other saved info is still in the camera settings like my name and all my saved settings. So not internal battery issue. What would cause error 2 randomly when inserting into the camera and it wiping out the file number?
I did a camera reset. I didn't have very complex settings. Could this have happened by inserting and removing the card with the camera powered on?

Apparently error 02 is "camera cannot access the memory card" - presumably either physically by way of contacts not contacting, or circuitboard problems, or by memory card failure (which could be intermittant)
It shouldn't matter if camera is powered on or not though, as the memory card door has a microswitch that powers the camera down when opened.

not really much a user can do apart from replace the card, and if still happening you might need to get a service tech have a look at it.