By Steve Grisetti:
It's always a better strategy to create a large project in small pieces and combine them in a final mix into one large one. Doing so uses your resources much more efficiently and greatly reduces potential technical problems.
The process is simple:
1) When completed, export each segment as an AVI movie by using File/Export/Movie.
To avoid losing quality by recompressing the already compressed DV-AVI files, after you File/Export/Movie, click on Settings and, under the Video tab, uncheck the Recompress option. Doing this also saves output time since, DV-AVIs that have no effects or transitions applied are simply copied as is into the new file.
2) Open a new project and import each of the segments into it using Add Media.
Not only does working this way break everything into much more trouble-free bite-sized pieces, but the final mix requires virtually no rendering and saves a lot of processing time.