errormessage when add a new page from versions

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I ge this erormessage when i add a new page from Versions (ad page ), and shall publish the page. A errormessage i dont get in 5.7.3.1 . Here is the errormessage:

{"error":{"message":"Call to a member function publish() on a non-object"},"errors":["Call to a member function publish() on a non-object"]}

Someone who knows why???

Falconova