
If you really want to use both, be sure to create different photo libraries for both apps so they do not overlap while both in use. Though it’s certainly possible to run both iPhoto and Photos app on the same Mac, it’s best to not try to juggle using both the apps so as to not confuse or mess up an image library, users should really stick to one app or the other. You’re back in iPhoto, if you have a photo library it will show up, if you don’t, you’ll be on a fresh iPhoto screen like so:
Return to the iPhoto app in /Applications/ and launch it as normal, you may want to drop the icon into the OS X Dock for easy future access. Click on “Install” next to iPhoto, this will download and install the newest version which is compatible with OS X 10.10.3+. Go to the “Purchases” tab of the Mac App Store and locate “iPhoto”. Open the App Store if you haven’t done so yet when seeing the above error message. How to Run iPhoto in New Versions of OS X There’s a pretty simple fix to that series of errors however, and in just a moment or two you’ll be able to use the iPhoto app again if you wish. Download the latest version for free from the Mac App Store.” but when you click on “Search App Store”, you’ll get an error saying “Item Not Available”. The version of iPhoto installed on this Mac is not compatible with OS X Yosemite.
Most commonly, Mac users will encounter the following error message when trying to launch iPhoto on a Mac with Photos app: “In order to open “iPhoto.app”, you must update to the latest version.