It will be best to remove the OOBE and MBLStore and try again.
Make sure to close all Adobe applications before starting the steps to resolve this.
For you reference here are the locations for the OOBE and MBLStore folders:
In both situations get rid of the double quotes for this to work.
From experience I can tell you that removing Muse from "Programs and Features" in Windows or from "Appications" on Mac did solve the problem for me.
I hope this will help you sort the issue.
I've tried all these steps and still have the same problem.
I launch Muse, click either the 'Try Adobe Muse for free' or "Sign in to an existing subscription' and automatically get the following error:
An unexpected error occurred.
An unexpected error occurred processing your request. Please try again later.
I'd really like to use Muse. Can you please help?