With Mac OS X, version 10.10.4 you need to update iPhoto to version 9.6.1
The problem is, that these updates are only available from the App Store and not from Apples Support Downloads page.
But because Apple stopped selling iPhoto, the AppStore does no longer offer iPhoto updates.
You can only update by reinstalling iPhoto from the Purchases history at the App Store. Sign into the AppStore with the AppleID you used to buy iPhoto or update it in the past. Move your incompatible iPhoto to the Trash, but don't empty the Trash. Then Reinstall from the fourth tab (Purchases). (the method is described in this user tip:
Get iPhoto 9.6.1 if you didn't update before OS... | Apple Support Communities).