WebOffice author dynamically connects to your ArcGIS Server (Server Object Manager process, SOM). In order to be able to successfully connect to ArcGIS Server, the Windows user you are logged in must be member of the local Windows user groups agsadmin and agsusers on your ArcGIS Server machine.
If the connection to the ArcGIS Server does not work then you will see an error message like in the screenshot below.

WebOffice author 'Access denied' message - no connection to ArcGIS Server possible