Numbers file locked up
So I'm working on a file and it is suddenly locked up. I can't do anything with it. I exited Numbers and re-launched -- no result. Restart computer -- no result. What to do? Numbers 3.5.3. I'd attach it to this question but there is apparently no way to do that. Any hints? MacBook Pro, OS 10.10.4. thanks
Numbers 3.5.3