Solved co-authoring failure for Office 2016 users causing locked documents

Users keep getting locked out of a document.
A user is able to make changes, but then everyone else isn't.

Among the errors:

"We're having trouble connecting to the server. If this keeps happening, contact your help desk."

"Upload failed. This file is locked for editing by ..."

Fiddler displays a 404 cobalt error:


Apparently, there is a key in the registry that if non-existent, will prevent co-authoring!

There is a hotfix, the October 13, 2015, update for Office 2016 (KB2920679).

Or simply add the following registry key, and then restart Word:

Windows Registry Editor Version 5.00


(this could be saved as a .reg and executed)



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