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Read this article to know how to resolve the "Associated site is not available to this user" error when publishing to Business Catalyst.
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Error "Associated site is not available to this user" when trying to publish a Muse site to Business Catalyst after updating to Muse CC 2015.2.

Reason
Issues with associating the Muse user account with the corresponding Business Catalyst user account is causing this issue. Because of this disconnect, Muse is not able to list your existing Business Catlayst sites in the Publish to Business Catalyst dialog box.
Workaround Solution
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Publish it as a new trial site to Business Catalyst.
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Close and reopen Muse.
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Open the affected Muse site.
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Publish to Business Catalyst.
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