I have done a search but cant really find the same issue I am having, I purchased a used 5d MKii, its in good condition and was to be a work horse for sports event shoots.
First night took it to use, put in a cheapo CF card, it gave an error 02, I thought oh maybe a duff card, put it to one side and tried another card, that worked that night an no issues, just tried using it again and as soon as I put in a card I get 'Not formatted, format card', I can then format it no problem in the camera, then take shots, play them back ok. Take the card out and put it straight back in and it gives either Error 02 or card not formatted straight away or seems to be ok until you shoot then error 02.
I tried a Lexar, a Sandisk Extreme and a cheapo Ultima card, all work find in my 7D even for large shoot at running events.
I can understand a card fault but one where you can format the card and use it but cant take it out the camera or else the camera refuses to read it again properly ?, never seen this.
Anyone got any ideas ?, I have contacted the place I got it and it can go back for a refund or replacement but just curious if their is anything I am missing before I get another one and find out its something I am doing ?, I can see how they missed it, they put in a card, took some photos, checked them on a PC and everything was OK, quite possibly never put the card in the camera again.