Library won't open

Question

I have tried rebuilding and continue to get the message that the library is either in use by another application or have become unreadable. What things can I try to resolve this?  I didn't make any changes to the computer to cause this to happen.

Answer 1

That's more than enough free disk space. So the new library that iPLM created is stalling out after about 5 minutes of use, right? 
Log into another user account on your Mac, create a library (or use the one there if there is one) and see if you can duplicate the problem.  If you can then the issue is system wide and will require a reinstall of iPhoto or the system.
If the problem doesn't happen in the other account then your account is the culprit. First  make a temporary, backup copy (if you don't already have a backup copy) of the library and try the following:
1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your
     User/Home()/Library/ Preferences folder.
2 - delete iPhoto's cache file, Cache.db, that is located in your
     User/Home()/Library/Caches/com.apple.iPhoto folder. 
Click to view full size
3 - launch iPhoto and try again.
NOTE: If you're moved your library from its default location in your Home/Pictures folder you will have to point iPhoto to its new location when you next open iPhoto by holding down the Option key when launching iPhoto.  You'll also have to reset the iPhoto's various preferences.
NOTE 2:  In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.