"Can't remote connect to an older version"? Both versions are the newest!

I have been using Team Viewer Free Remote Management for years without any problems.  This morning I tried connecting to my Father's computer but I kept getting a message that I couldn't connect because he had an older version of TeamViewer.  He tried to  "Check for New Version" and it said his version is "Up to Date.  There is no New Version of TeamViewer".  I also have the latest version (14.7.1965).  I used Remote Management 2 days ago and it worked fine.  All of a sudden, it won'tconnect today.  What can I do?