The installed version of iPhoto is not compatible with the installed version of OS X

Certain versions of OS X enforce a minimum version of iPhoto that must be installed, and will refuse to run older versions. If this is the case, then trying to open libraries or perform other operations with iPhoto Library Manager will likely result in an error message saying that the installed version of iPhoto is not compatible.

Normally, it would be a simple matter of updating your version of iPhoto via the Mac App Store, but since Apple’s release of their new Photos app, iPhoto is now no longer available on the app store, which makes it impossible to directly update older versions of iPhoto. It is still possible for most Macs to get the latest version of iPhoto, but it now requires jumping through some hoops. To download the latest version of iPhoto:

1. First, make sure your backups are up to date, just in case you should need to revert or retry any of the steps here.
2. Click the Finder icon in the dock to bring it to the front, then select the Applications folder (or press command-shift-a).
3. Look for iPhoto in the list of applications - if it is indeed an incompatible version, it will likely have a circle with a slash through it displayed over the app’s icon.
4. Drag iPhoto from the Applications folder to the trash. Emptying the trash isn’t necessary, but you can do so if you need to clear up some free space.
5. Select “App Store…” from the Apple menu in the upper left corner of the screen.
6. Click on the “Purchases” tab. iPhoto should appear in the list of apps shown there, with an “Install” button next to it
7. Click “Install” to install the latest version of iPhoto from the app store.
8. If you’ve installed OS X 10.10.3 with the new Photos app, that will have also removed the iPhoto icon from your dock. If you wish to restore it, after iPhoto has finished installing, drag the iPhoto icon from the Applications folder to the dock to add it back in.

There are a few obstacles you may encounter when following these steps:

• Reinstalling will only work if your Mac shipped with iPhoto 9.0 or later, or you purchased iPhoto 9.0 or later from the Mac App Store. If your Mac came with an earlier version of iPhoto, there is no way to download the latest version of iPhoto from the app store. Your only options in this case are to revert to an earlier version of OS X that supports your version of iPhoto, or switch over to using the new Photos app (if you’re running OS X 10.10 Yosemite).
• If iPhoto doesn’t appear in the list of applications in the Purchases tab, it’s possible that iPhoto has been hidden from your purchases list. For steps on “unhiding” iPhoto, see this support article on Apple’s website.
• If the button next to iPhoto says “Update” instead of “Install”, you may have additional copies of iPhoto on your Mac that the App Store is finding. Do a Spotlight search to find and delete any other copies of iPhoto that are lurking in another location.
• If iPhoto still doesn’t appear in the purchases list after all of the above, try quitting and relauching the App Store, and/or restarting your Mac. Sometimes this is necessary to make the App Store rescan the installed applications and present the correct options for downloading and reinstalling.