[516] The Client could not access the remote application

We have a user who has two Windows machines on his network. One connects to the software we are hosting via RAS perfectly, the other throws the attached message when using the RAS desktop client (works perfectly wee in the HTML5 client)
He has fully uninstalled and re-installed the RAS client, to no avail. What could be the possible cause of the Desktop client failing when the HTML5 one is fine?

Many thanks.

 

Hello, what is your Parallels Client version?

 

V16.5 (build 20264)