I would try deleting that patch and redownloading it. Did you use the official downloader or a torrent? If a torrent, could you have installed the downloaded patch into the wrong directory?
Generally I use a torrent, but this was a small update so I did the official downloader. I don't think it would have made it to the install process if it was in the wrong directory though.
I tried deleting and downloading again, but the same error. Now I'm trying as a torrent but not finding any seeds.