Exporting Problems

I'm on all the standard settings on FCP 7 and am on RT. I tried to export the video I created to a Quicktime Movie and when it finished, I looked back at the video only to find out that there are parts where it jitters back and forth, has random green frames (that I did not put in), and pixilated images. This has happened to me recently on another project. I still have all the footage and nothing is lost, so is there any way I could fix this? Thanks.