Dealing With A Corrupt iPhoto Library

There are sometimes when your iPhoto can, for one reason or another, become corrupt and unable to use. Various symptoms can include your photos not showing up properly (e.g. showing up as gray or black squares), the library becoming unusably slow, or iPhoto crashing as soon as you try to open your library. There are several steps you can perform to try to get your library back into working order.

iPhoto's built-in rebuild function

iPhoto contains a built in method for rebuilding a library's database and/or thumbnails. The steps and results of rebuilding differ depending on what version of iPhoto you're running, and the nature of the problem with your library. Full instructions for doing a rebuild can be found on Apple's website here.

Permissions problems

One other common cause of this is that the permissions for your library folder or its contents have been turned off so that iPhoto can't read the data it needs. First, try restoring the permissions of the folder by doing the following steps:

Select the library in iPhoto Library Manager and click the Options button on the right
Select "Read & Write" in the "Owner" pop-up menu and click the "Apply Permissions Now" button. This will make your library folder readable and writable. Then click "Done".
Note that if the library in question is owned by another user on the machine, you may not be able to successfully reset the permissions for the library. In that case, you'll need to log in as the user that owns the library and try again.
Open the library in iPhoto and see if it now can read your album data

iPhoto Library Manager's rebuild function

iPhoto Library Manager includes its own rebuild function which can attempt to rebuild a corrupted library based on the information found in the AlbumData.xml file. You can read more about this rebuild function here.

Extract and reimport

If the above methods aren't helpful, the last resort is to extract the photos from your library folder and then reimport them into a new library. The disadvantage to this method is that you will lose all your photos' metadata, albums, and other organization from iPhoto, but you should at least be able to preserve the photos themselves.