Comment 1 for bug 1255285

Do you have given the same name to this project ?
You should remove in the hidden folder openshot in your home, the file called pid.lock. If you don't find it in, you could remove directly the folder but you'll loose all that you have in (i.e Blender files generated, Transition imported,...).
At the next start of Openshot, it will be recreated.
That's could resolve your issue.