Hi xblitz and thank you for your reply. Perhaps it is necessary to start from the scratch; I have installed duplicati in this way:
In this server there are many users and I don’t want to specify for everyone which directory to backup, so I have created this template like in the picture below:
My goal is to backup desktop folders, documents, favorites, google drives, etc., but not all users have the onedrive or thunderbird folder … for this reason I use filters.
Moreover this picture showes that I have enabled snapshot to avoid any error during backup of used files like word, outlook or any other software (I have installed Duplicati like a service):
I want to specify that the error is appeared only in this server (I have many installation of Windows 7,10, Server 2008R2 and Server 2012R2) but this is my first Windows Server 2016 and this is the first time I have met this problem.