I just finished upgrading our "test" environment from 9.14 to 9.20 and everything seems to be running okay, the only issues I just ran into this very particular issue.
I can login to the Desktop Workbench without an issue but when I try to edit a user I get the following error: The HP Project Management server is down or unreachable. Please contact your HP Project and Portfolio Management system administrator. (KNTA-10035) the full error is attached.
I have tested opening the workbench from the site and editing a user and was able to do that without an issue, I have also tested opening the workbench from a different computer without issues as well.
(Prod and Dev are working fine without an issue even though they are 9.14)
When I have had problems launching or running the workbench from the desktop, the only reliable solution was to open the Java Console, delete the entry for the workbench, and rebuild it from the PPM Dashboard.