FCPX inserting a single solid green frame

I'm sometimes getting a green flash in videos I'm exporting from FCPX 10.0.7. It's a single green frame, and so far has always been in the first 30 seconds of the hour-long videos I produce.

I am using FCPX's "share" command to export (and I'd like to avoid purchasing Compressor if I can). I can pause the video and park my playhead on it, so I'm thinking it must be a rendering issue rather than a playback issue. The flash shows up in both the exported Quicktime movie and, after the export process, in the FCPX timeline. I don't have any plug-ins installed, and I don't have a second graphics card or second monitor, so the problem in this knowledgebase article would not apply.

My computer: MacBook Pro early 2008, 2.4 Ghz Intel Core 2 Duo, 4GB RAM, running OS X 10.8.2.

Any ideas about how to avoid these errors? Thanks in advance.