Has the iPhoto picture folder or iPhoto application been moved from it's default location?
Here is the standard first aid.
There are several procedures to try. Please try in order. Also, unless otherwise noted make sure you have Quit (closed) iPhoto.
1. Restart your computer to repair the directory if needed.
2. Run "Repair Permissions" from Disk Utility located in your Applications>Utilties Folder.
3. Try iPhoto again. If it doesn't work then QUIT iPhoto.
4. Your iPhoto preferences file may be corrupted.
(MAKE SURE you QUIT iPhoto first)
You will find it in your Home directory:
(Home/your account) >Library>Preferences>com.apple.iPhoto.plist
Remove or trash the preference (.plist file) and restart iPhoto.
If it still doesn't work go on to these remedies, in order.
5. Bad Album data?
1 - move the Albums folder and the AlbumData.xml file to the desktop.
2 - launch iPhoto. It if launches successfully you probably have a corrupt album.
To locate the bad "aibum", do the following:
1 - move one of the individual album folders and it's associated data file into the new Albums folder that was created in the iPhoto Library folder.
2 - launch iPhoto. If it's successful do the same with the next album folder and data file. If iPhoto doesn't launch successfully, that's a bad one and remove it and the data file.
3 - repeat for each individual album folder in the old Albums folder.
6. Rebuild Library
QUIT IPHOTO FIRST
Relaunch while holding down the key combination below for your version
Option+Shift IPHOTO 2
Command+Option+Shift IPHOTO 4
Command+Option IPHOTO 5