I have this recurring problem. Motion 5 won't launch.
I constantly have to go to the finder and Force quit. Tried resetting preferences but it doesn't work.
Maybe once in a while it will launch but, just now, tried 3 times with no success.

Will removing and reinstalling help?
Do I simply trash the application and preferences?

I am about to move all my compositing to FCX!

UPDATE: Uninstalled and reinstalled...Works for now.
Thanks,