Happy to report nothing has changed with Lightroom CC 2015.
I'll try the method suggested in this thread (importing via Lightroom 5): Re: Major Problems Using Aperture/iPhoto Importer Plugin in Lightroom CC
Okay, that made zero difference.
Still open to ideas, friends.
Can you please try to export images from your iphoto library to the desktop and then import the images into Lightroom.
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Thank you for the idea!
After some further research, I've decided to leave the iPhoto library as is, create an alias of the Masters folder outside of the iPhoto library package and import from there, rather than duplicate the library.
Here's hoping this doesn't come back to bite me in the future!
I would love an answer to this question since I am getting the same error trying to import my iphoto library into Lightroom 5.7.1.
This question was also posted by another user on Lightroom Forums in February 2015 and it is also unanswered. I guess no one knows the answer.
I guess it depends on whether you have an iPhoto referenced library or manged library. I think most people have a managed library. Apple hides the masters in package contents for good reason. To prevent corruption of the iPhoto library. I have no idea how an alias would work but if the same images are being referenced from two applications (LR & iPhoto) there must be room for things to go wrong, especially if one of those apps is writing metadata to files.