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Changing Music Library - An unknown error occurred (--42076)

I'm assuming this is a fairly common predicament due to the sizes and costs of new Mac internal SSDs. I have an aging Mac with 1 TB internal drive, and I'm replacing it with with a new Mac that has 500 GB internal storage. The only item that's too big to fit on the 500 GB is the iTunes library - about 870 GB. I don't subscribe to Apple's Music.app. I copied the Data volume of the older computer (which appears to be working, just slow) to an empty 1 TB SSD using Carbon Copy Cloner 6, then (working with the old system still) used the instructions at https://support.apple.com/en-us/HT210230 to select the library from deep inside the user folder on the external drive. The items appear in the Music main window, but I received an error message: "An unknown error occurred (--42076).", and playing the items doesn't seem to work in Music.app. Carbon Copy Cloner is the only way I've found to copy the library to the external drive without error, because when I use Finder, the process stops before completion with various errors. The old Mac has been upgraded as far as possible, so I'm using Catalina.


Is the answer to wait until the new computer contains all the migrated data except the internal Library folder (I would have to delete that before migrating to accommodate the smaller drive, right?)? In other words, is Monterey less likely to produce that error?


Am I instead going to have to re-add the media files to TV.app again once I have successfully selected an empty library on the external drive?

Posted on Jan 29, 2022 5:10 PM

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Posted on Jan 30, 2022 11:54 AM

I used the tar command line utility to copy the entire contents (870 GB of data) of the folder containing the .itl file to the root level of a cleanly APFS-initialized 1TB external volume. That wasn't very fast (2012 21.5" iMac), but tar didn't have the problems that Finder had when I tried it before. Then I deleted the media on the iMac to avoid problems with the disk space required by Migration Utility on the new 500 GB drive. After migration was complete, using the instructions at https://support.apple.com/en-us/HT210230 to select the external library on the newer computer was successful.


Also, I see in my original post that I referred to the Music app first, then later, the TV app, so I understand why my question was confusing.

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Question marked as Top-ranking reply

Jan 30, 2022 11:54 AM in response to llee

I used the tar command line utility to copy the entire contents (870 GB of data) of the folder containing the .itl file to the root level of a cleanly APFS-initialized 1TB external volume. That wasn't very fast (2012 21.5" iMac), but tar didn't have the problems that Finder had when I tried it before. Then I deleted the media on the iMac to avoid problems with the disk space required by Migration Utility on the new 500 GB drive. After migration was complete, using the instructions at https://support.apple.com/en-us/HT210230 to select the external library on the newer computer was successful.


Also, I see in my original post that I referred to the Music app first, then later, the TV app, so I understand why my question was confusing.

Changing Music Library - An unknown error occurred (--42076)

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