Hi, Vincent,
Could you describe your situation in more detail, and what you are trying to do? In what version of iMovie was the project created, and do you still have the app on your computer? As Jim says, you cannot import the project itself into iMovie 10.1.8. The only way to open and edit the project is with the old version app in which it was created. Or, you could export the old project with the original app into a Best Quality Quicktime movie and import that into 10.1.8, where you could do some limited editing, such as splitting and adding new clips, adding titles, audio, etc.
-- Rich