This is a classical story.
Given you cannot import one project file (project.prel) into another.
1. Export the Timeline of the first project to an appropriate file format and then import that export into the second project with the appropriate project preset.
2. You should do OK with version 10 with the ClipMate program for the copy/paste insert between two projects.
Please review and then let us know if any of that worked for you.
Please do not hesitate to ask if you need clarification on anything that I have written.