How did you try to open the Aperture Library, Victoria?
Did you double-click it in the Finder and then get this message?
If that does does not work, can you open it with the Aperture Library First Aid Tools, by holding down the key combination⌥⌘ and double-clicking?
If the above does not help, try Frank Caggiano's tip and remove the iPhotoLock.data from your Aperture Library, but be careful, not to delete anything else. Do you have any backup of your Aperture Library at all? See: