iTunes glitch with movie artwork

I have one movie (can't recall source) where it doesn't have any artwork and multiple attempts to paste an image into the info|artwork window or using the "add" button doesn't stick. All other movies are fine. After hitting OK nothing changes. Going back to "get Info"
shows a blank artwork window.

Ideas?

Anybody? I'm pretty sure I downloaded the movie from iTunes using a DVD digital copy coupon. One would think I could re-download it as though I had purchased it (assuming the problem lies in a corrupted file) but iTunes does not show that I own it, so to download again would require purchasing it.