Connection could not be established. Teamviewer not running on partner computer.

Windows 10. Teamviewer 13.2.5287 (July 23 2018 09:22:40)

I get the subject error message from Windows 10 using the Teamviewer desktop app.  But it cannot be accurate because I *can* connect to the partner computer with Teamviewer on an Android tablet.  I can also force a connection to the partner computer from Windows 10 if I use my browser (Chrome) and request a connection from the web page.  Then the browser apparently starts an instance of the Windows 10 desktop Teamviewer app, which connects succesfully.  

I want to run the desktop app directly or Windows 10, without using the browser.