I have Windows 8.1. I get the following message: "Cannot Start Microsoft Outlook.  Cannot open the Outlook Window.  The set of folders cannot be opened.  the file C:\Users\David\AppData\Local\Microsoft\Outlook\***@outlook.com.ost cannot be opened."  *** is inserted in this body solely for security reasons.

Hi,

This issue can occur if the Navigation Pane settings file becomes corrupted. We can try reset the file by starting Outlook using the /resetnavpane command-line switch. To do this, press Windows key + R to open the Run command, type outlook /resenavpane and press Enter.

Please let me know the result.

Regards,

Steve Fan
TechNet Community Support

The funny thing is a week later I was able to open Outlook (I had moved the .ost file to another folder).  But it would not download from the server.  So I moved my old .ost back to the proper folder and it started downloading from the server again.  In the meantime, I have a few weeks of emails on my Thunderbird.  Since Outlook synchronizes to the server, I'm fine.