5D Mark 3 problem

I've owned my 5DM3 for about 4 months now and have found a problem and am wondering if anybody else has this issue.

I was shooting a party on Friday 2/22, all normal shooting (nothing in burst mode & the camera never got even warm) and all of a sudden the shutter stops firing.  The remedy that I found to elivate the problem is to open the CF door and close it.  I can then start shooting again till the next time the shutter stops.