So I just now, for the first time with FCPX, experienced the same problem.
I was option-dragging to copy a generator and text so I could use it again later in the timeline, and I got the beachball of death.
FCPX crashed, and now, after discovering the wonderful program Event Manager, I’ve learned that everything is well EXCEPT THAT PROJECT FILE.
A backup wouldn’t have saved me if I had it, because all my editing today is toast. The autosave file won’t launch, either.
FCP simply won’t launch when it sees that Project.
This…is bad. If anyone has determined how to “un-corrupt” a Project file, I’m all ears…er, eyes.