I deleted all of iPhoto application files... using "AppZapper". Installed iPhoto 5.... the application was stable but it would not read my iPhoto 6 photo library.
I upgraded from install CD to iPhoto 6 while keeping the same photo library. I got the repeat of iPhoto unexpectedly quiting. I sent the crash report to Apple through the "crash reporter"... no reply from them...
I asked the backup software developers of "SuperDuper", Dave Noonan to see if there is any reason for the quiting to occur after a restore from the backup files it made. I sent him the crash log of iPhoto from which he said that iPhoto was trying to read an iTunes XML file and so quits unexpectedly. I did what he suggested to rename the iTunes XML file and ran both iTunes and iPhoto sequentially but had the same result of unexpected quiting of iPhoto. Although, I must say I tried this only once...
I thought the the lack of space on my hard Disk may be the cause of (some of) my problems. So I used "CleanApp" (instead of AppZapper) to delete or archive applications I do not use. This included GarageBand that took up 3.5Gb of space... When I had deleted as many as I could and had more HD space freed... I ran iPhoto again... To my surprise, the iPhoto worked OK and so far there are no problems... I rebuilt all the thumbnails etc as there was some mismatch in them...
In my view, it may be that the CleanApp deleted some file that iPhoto was reading that resulted it to quit unexpectedly. But Dave Noonan said that was not what the iPhoto crash report indicated. It was clearly the iTunes XML file that iPhoto was trying to read... I would have to except it that he is right... (as he has the benefit of making sense of the iPhoto crash report)
I looked up Apple Support and found there are many instances of iPhoto quiting unexpectedly so it must be a common problem...
So, if it happens to you... I hope this post will help... to me family photos (and keeping them accessible and in order) are something more valuable than the Mac..
FiL