Hi Sfar, thank you so much for your efforts.
I think I must have had a number of corrupt files. I trashed all of the AIF files waiting to be added to my library, and re-converted the original FLAC files. After doing this, I am now able to add the AIF files to my library.
How the files became corrupted, and why none of my software was able to detect they were corrupt is a mystery to me. It must have been pure coincidence that their corruption coincided with the iTunes upgrade.
I think I must have had a number of corrupt files. I trashed all of the AIF files waiting to be added to my library, and re-converted the original FLAC files. After doing this, I am now able to add the AIF files to my library.
How the files became corrupted, and why none of my software was able to detect they were corrupt is a mystery to me. It must have been pure coincidence that their corruption coincided with the iTunes upgrade.