what type of media are you using? I’ve had a similar problem when using mainly motion files. I don’t know if there is something screwy with the way FCP reads 20ish motion files but other projects opened fine just that one would crash my computer.
If the camera has a memory card for stills, use that. move take picture move take picture… when card is full open quicktime PRO and open image sequence (the pictures you just took). choose frame rate and make movie. the most simple way I’ve found.