Itunes problem: disappearing art

There are two tracks in my Itunes library that seem unable to “hold” artwork. I go to the appropriate window, and add the art and it looks like it’s there. But as soon as I hit “OK,” it seems to disappear, and when the track is played, there’s nothing, and, indeed, the artwork window is black.

Anyone experienced this problem?

Possibly a stupid question, but it’s always good to check: Is your artwork display set to “Now Playing” or “Selected Item”?

That’s not really an issue. The artwork is gone on those two tracks and those two only. I open up the “info” window, and the artwork that I had added just is not there. It’s there for the remaining 5,300 tracks in Itunes.