I started the "I am flabbergasted" discussion that also deals with this issue.
And here is a more definitive reply.
I telephoned Apple (my new machine still had a few days of telephone support) and spoke to a senior adviser.
He said I should have updated iPhoto from 9.6 to 9.6.1 BEFORE upgrading Yosemite from 10.10.2 to 10.10.3 - as Yosemite 10.10.3, because of "Photos", puts a no-entry sign on all previous versions of iPhoto. So if you can still do this, it's the lightest solution.
He recommended deleting all instances of iPhoto, which I did (of course I kept copies elsewhere), I checked with Spotlight that indeed all copies were gone, and then launched the AppStore - Purchases. This time, for iPhoto, instead of an inoperative grey "UPGRADE" button there was an "INSTALL" button.
This duly installed a new iPhoto 9.6.1.
I had thought it was the presence of the new "Photos" that was stopping the update of iPhoto. Not so, it was the non-recognised iPhoto 9.6.
Many thanks indeed to a particularly helpful Apple Senior Advisor (all in French by the way - I live in Belgium).
Further comments:
- I also have Canon ImageBrowser and Image Capture on this machine, Yosemite 10.10.3 - ImageBrowser woks, I haven't yet tried ImageCapture. I can't remember when I last updated them from the Canon web site.
- At one point I had to go all the way back to a pack I had bought for Snow Leopard with iWorks and iLife bundled, in order to gradually upgrade their applications to, for example for iPhoto, version 9.6.1. I found the links I needed thanks to these forum discussions, not thanks to either the App Store or the Apple Support pages. I even have iWeb 3.0.4. Although I now use other software for web pages.
- Photos - a huge backward step, but the Apple Senior Adviser I spoke to felt pretty sure it would evolve - yes but in the meantime it is essentially unusable. I just hope Apple will not finally debar all use of iPhoto etc. in future OS X releases. If so, I shall have to also migrate to things like Lightroom.
Nickiwi