Optimizing clip ruined my footage and turned it to solid green screen. Help!

When I tried to change the speed of clip, imovie prompted me to optimize the footage as the only way to change the footage speed. I checked ok to optimize, but now I can't view the footage! I can see the thumbnails of the original footage as thumbnails, but my I place my cursor over the thumbnail or try to play the footage, all I see is a solid green screen. The audio is still there, but the picture is gone, gone, gone. Is there any way to recover the original footage? 😟

Thank you!