Solved co-authoring failure for Office 2016 users causing locked documents
Problem: 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: Solution: 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 [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\FileIO] "EnableRealtimeChannel"=dword:00000000 (this could be saved as a .reg and executed) Source: https://support.microsoft.com/en-us/help/3100925/word-2016-co-authoring-fails-when-file-is-stored-on-sharepoint-2013