Iphoto isn't working on my macbook pro

Question

Iphoto isn't working on my macbook pro, it is coming up with the following message:-
Your photo library is either in use by another application or has become unreadable.
Shut down and restart your computer, and then open iphoto again.  If the problem persists, try rebuilding your photo library.  To do this, quit ipoto, and then reopen it while keeping the optino and command keys pressed.  You can also try restoring your photo library from a backup.
Please help.  I don't want to delete this app and then have to pay for it again.

Answer 1

Restore from your back up is a good place to start.
Failing that:
Download iPhoto Library Manager and use its rebuild function. (In early versions of Library Manager it's the File -> Rebuild command. In later versions it's under the Library menu.)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.