Corrupt MOV file

I filmed a wedding last weekend and used a number of 32GB Extreme SD cards in my 60D and a 16GB one in my H4n. All great except for one .MOV file on one of the 32GB cards that didn’t copy. It would get about 90% of the way there and then freeze before it gives up. If I play the file in the camera, it starts from halfway through the clip but plays fine until just before the end when I get an error 70 which needs me to reboot the camera. If I play it from the card reader, I get a choppy version of the whole clip.

I’m not sure if it’s the same card (hadn’t numbered them by then), but when I got this batch of cards, I did some test shots and one of the 32GB cards got to the point of maxing out its buffer and auto-stopping the recording after a few seconds.  At the time I thought it just needed formatting and assumed I’d fixed it.

Am I missing something? Is there some diagnostic test I could use? or is it just a duff card?

Thanks for your help!