I had a recording that occured when my fios box wasn't properly connected, so all that's in the recording is a "no signal" message.

It's a show that's often repeated, so I tried clicking "forget old" so it would record a new one - but nothing changes. "Forget old" is still there as a choice, and it won't record a new instance of the episode.

Under manage recordings there's a way to purge it's memory of past episodes either selectively or for a whole title.

I'm far from my box but if you can't find it in the FE menus someone should be able to provide the path.