I had this exact same problem.
It has only happened once, a set of about 8 sequential images taken wandering through the audience at an outdoor rock concert.
The corruption started as a few small lines of pixels, worsening in every shot until it was as bad as the OP, then the corruption lessened until it was fine again.
I'd already spotted that the embedded jpegs are fine.
5DII, Sandisk Extreme, LR3
I was assuming RF interference as there was an awful lot of equipment around the site (10000 audience, inside a park)
But I'd visited that spot at other times during the evening and those shots were fine.
And I shot about 800 that evening in total including others taken from the same spot.
Never seem the problem before or since.
I deleted most of the corrupted images and only kept a couple for reference.
I'll try the 1:1 preview trick and report back.