Read this troubleshooting article to resolve Shared Unknown Error when publishing using Business Catalyst in Adobe Muse.
When you publish your site using the Publishing to Business Catalyst option, you see the following error:
"An unknown authentication error has occured using your Adobe ID (SHARED_UNKNOWN_ERROR)

Unknown authentication error while publishing Adobe Muse sites to Business Catalyst
You experience this issue when Adobe Muse and the Creative Cloud Desktop application go out of sync. You may also experience this error if you sign out of Creative Cloud while working on Adobe Muse. In this case, if you do not see the Sign in window immediately, and if you continue to publish using Business Catalyst, you might see this error message.
Read on to know the resolutions for this issue: