Q: iTunes error message

I have a MacBook Pro running Sierra. Even when on Yosemite, I've been getting an error message when I try to download (from iCloud) songs that I've purchased. I have iTunes Match.

I want to say that this is incredibly frustrating. I've found iTunes to be Apple's worst ever product over the years. Full of bugs, confusing usability, errors like this where I can't access music I've paid for, etc.

Thank you for any advice on how to fix this. Yes, I've given read and write permission to my entire hard drive, but may have deleted a few "wheel" permissions before doing this.

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