iMovie Library permission denied on my MacBook Air

I'm trying to open a library I created a few months ago for a new business. I can see it on my Mac, I can double-click it, but when I do, I get "could not be opened. Permission denied." It says it's already in use by ME on MY computer. Well, that's funny because I'm not able to access it! What is happening here? I've read previous discussions on this and it says to check the read/write permissions which are all set to read/write (get info). Now what?

[Re-Titled by Moderator]