I have this same problem with my Canon 60d.
Even using Class 6 Kingston also have this problem from time to time.
Upgraded to Imation Class 10, also have the same problem.
I read somewhere that the problem will surface if you had deleted some shots or videos on that card, to prevent this from happening, you should not delete any shots/videos until you have finish all the shooting you want.
i'm using 60d with sandisk 32gb class10 for my video recording.
so far so good, except for that one time when my recording goes over 12 minutes, the recording stopped automatically.
if you have ensured that your card is class 6 and above, do make sure that your video recording doesn't go over 11 minutes 59 seconds.
this is a limitation of dslr recording videos. i think i read it somewhere in the manual of the camera also..