FCP7 crashes when left overnight rendering/exporting - please help!

When I leave FCP7 exporting or rendering overnight, by the morning it has crashed with the error message: "Final Cut Pro quit unexpectedly while using the Final Cut Pro plug-in" - I've tried trashing the p-list, full reinstall, everything short of flattening the Mac... Any suggestions?

It doesn't do it when I'm sat there watching it tick during the day... The only difference I can think of is that I switch my screen off, but I can't see that causing an issue.