iMovie 9.0.9 won't launch

I have a Mid-2011 iMac running Yosemite (10.10.3). I recently downloaded and installed iMovie 10 and upgraded to 10.0.7 I previously had iMovie 9.0.9. I have some videos I created using iMovie 9.0.9 which will not open in iMovie 10. I found the previous iMovie app in my applications fold and have tried to launch iMovie 9.0.9 to edit these videos, but iMovie 9.0.9 will not launch. I have deleted the preference files and restarted my Mac. I have removed iMovie 10 from my applications folder, I have even gone back into Time Machine to download previous application and preference files from my backups. Nothing is working. iMac 9.0.9 will not launch. How can I get a round this? What am I doing wrong?

Thanks for the help,

Paul