Motion seqs in FCP no longer rendering

Sorry about the double post - I put this in the Cafe LA forum, too...

I have several Motion sequences in my FCP timeline which mysteriously will no longer render (its a 30 second seq). This project is ongoing and up to this point, FCP and Motion have worked flawlessly.

I deleted FCP preferences, opened up a new project, copy and pasted the timeline seq into a new seq, still no luck. The render window will appear when I hit Command-R (or even Option-R) and it looks like its rendering - says "2 minutes to render", gets about halfway done and then speeds up at the end - but the seq in the timeline is still red lined. Using the menu render items doesn't change anything, either. Plenty of hard drive space, mucho memory, etc.

What's weird is that since I have been working on this project (three weeks) there have been zero problems - any help would be appreciated.

FCP 6.0.5
FCS 2
Leopard 10.5.7
2 x 2.66 GHz Dual Core intel Xeon
13 GB RAM

You could try right-clicking the Motion projects, choose Open in Editor, make sure they contain all links, and then resave the projects. If that doesn't work, you could always render out of Motion and replace the Motion project file in FCP with the rendered QT movie.