Help. Can anyone explain this?

Hi,

Can anyone explain this???

Relatively new 60D, but I've taken > 300 images so far, and this hasn't happened before.  This is the first time I've used my 70-300 f/4-5.6.  Could that be it?  Or the SD card?

It didn't happen to all the images.  Maybe three or four of the thirty or forty I took.

Thanks for any help.

-ira