iTunes error code 4001, - iCloud music library won't update on Mac?

[iMore Question]

iTunes error code 4001, - icloud music library won't update on Mac

I have had this problem at the (so I'm told) senior level of iTunes support for nearly a month now, with no solution yet forthcoming. I have about 52k tracks which I own and are on an external drive attached to my iMac (frequent backups to additional drive and to Backblaze). I also have about 21k Apple Music tracks, all carefully tagged and metadata-ed just the way I like them, which, for classical music, is a chore. However, about a month ago the icloud music library simply stopped updating on my iMac - whenever I tick the "icloud music library" box in Preferences/General, I get the same old result: the activity window shows the usual steps, "Gathering information, etc" followed by "Waiting for Apple to deliver your icloud music library", but then (after at least an hour or two) I get "Genius results cannot be updated right now, an error occurred (4001)". Naturally, we (Apple support and I) have tried all the entry-level solutions over the weeks, de-authorizing and re-authorizing, signing in and out of Apple ID, turning Genius on or off (I never use it and so the default would be "off"). I even tried to download the library to a different Mac user: pretty ugly, I just got one error message after another. This error message looks very similar to the way things were a year ago, when Match was limited to 25k tracks and one's library exceeded that, but I shouldn?t have that problem at my number of tracks. And another odd thing - the whole library shows up just fine, Apple Music and all (other than additions attempted since this problem), on my iPhone and iPad. So effectively, unless I use an iOS device, I can only see and play my "owned" tracks. Anyone else have a similar issue? And a solution?!

 

[chrysbar]

I don't know if you solved the problem. But I have a possible cause for this: you wrote that your media is on an external drive. Maybe you did something like I did: I had my media files on an external disk, but to make things go faster with iTunes, I put the iTunes library files on my quick internal ssd... And I just kept getting the 4001 or 4010 error messages; i found out that the 4001 means ERR_WRONG_FUNCTION_POINTER . The word POINTER seems to mean something points the wrong way.
Now that I copied all the itunes library files to the external drive, and then started the program from the new location, Apple Music is finally doing the job of collecting information from the iTunes library.

 

[chrysbar]

Well... that was a big disappointment! Before going to bed, the circle was more than 75% completed, but this morning, the error message was back and the iCloud library deactivated again.