Glitchy green frame appears over unrendered footage...

Hi All,

I am encountering a solid green frame when there are unrendered clips with composites in my timeline... I cannot scrub over the footage and see what the lowered opacity looks like, rather just get glitchy green and purple screens and other weird distortions. This happens with not only fades/composites, but also happens with effects and transitions. The footage is from a Canon 60D and I am editing in ProRes 422 on FCP 7. Anyone have a clue what this could be? Thanks.