Let's try 2 things and see what happens.
First, repair Permssions. I read about this error and most seem to fix it by repairing or modifying permissions.
Go to your Go menu in the Finder
In here, choose Utilities.
In the Utility folder, open Disk Utility
Click on First Aid tab and then click on Repair Permissions.
Wait for it to finsih, it will take a while and appear to hang. It isn't hung, just going through 100's of thousands of files.
When it completes, Quit Disk Utility. Try your task again.
If it still acts up,
go to your Applications folder. Click once on the actual (not alias) iPhoto application icon and then go to the Fie Menu and choose Get Info.
Click on the section called Sharing & Permissions.
If the section is grey, click the lock and enter your Admin password.
Look at the permissions for this app. It should look like mine in pic above. If not we need to change it.
Let me know,