Renders need Re-rendering

Do your renders in FCP's Timeline suddenly seem to un-render themselves? A friend called me a few moments ago in a panic saying that FCP was freaking out and un-rendering, seeming at random.

To make a long story short: he didn't realize that a previous project's test Render Files folder was still being used by FCP...while it was in the Trash.

Solution: Drag it out of the Trash or tell FCP to use another folder (stay organized, though).