I'm using iMovie '09 on 10.6.8, have hundreds of hours of green screen experience..

suddenly, I can't use the green screen filter.

I start a project as usual, drop a background picture into the timeline, then when I drop my green screen footage over the background, I don't get a "green screen" option as I should, only the option to "replace" or "Insert".

The same's happening in other projects I've already finished, so I can't edit them.

I've restarted iMovie, rebootd, no change.

Any help please??