I saw your post on the 'The Old World' mod page.
I had exactly the same error as you did.
You have to MANUALLY DELETE Mixu's unlocker, unsubscribe, and then re-subscribe. The unlocker had a new update recently but for some people it is not updating automatically. And not even updated manually unless you first delete the original.
Hope this helps.

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▄░▐░░░▄▄░█░▀▀ U HAVE BEEN BANGED BY THE
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░░░░░░▐▌▀▄▀▄▀▐▄SPOOKY BOOTY BANGER
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