word: non-admins can't update documents on webdav server, admins can

Question

A customer of ours is using a kind of sharepoint (not sharepoint) -a document repository- that, for what I saw, uses webdav .

There are two terminal servers, one of them is Windows 2008 R2 Datacenter v6.1 build 7601 , Office 2016 , and Internet Explorer 10.0.9200.17609IS . They couldn't access anything at all , they went as far clicking "edit" on the site and then Word they that he's sorry because he couldn't open the document.

I've fixed that , I added the site to the Trusted Sites list, and disabled SSL 3.0 and TLS 1.0. Local admins can open and update documents . Non admin users can open the document but not update it , and by can't I mean that Word opens the document in read-only mode and any attempt to switch to read-write will save the document in the local computer.

Now, the other server, Windows Server 2012 R2 version 6.3 build 9600 , Internet Explorer 11.0.9600.19867 , the former fix did the trick for both admins and non-admins .

Does anyone know where to look?

Thanks, Max