AFAIK you couldn't access files directly on the sharepoint because they aren't really there - at least not how they are displayed from the browser or explorer. What you see are just meta-data respectively a reference to the real data and you need to ask the "door-keeper" to get it. To communicate with the door-keeper you need a tool like your browser or the web-connector.
I'm far away from being an expert to this topic but I suggest to browse with your user respectively this user which is used within the connector if you could get access to the file which would ensure that your wanted file really exists and there are also proper access rights. The next may be to open the web-connector and getting access with them to renew all needed things with this wizard. Maybe the unique-id from the file changed or like you assumed the access-token is broken or needs a renewed authentication.
- Marcus
