"the connection was closed remotely"

Hello

Just installed VNC Viewer 7.11 and tried to connect to a remote HMI

the error i get is "the connection was closed remotely"

VNC server conenction is enabled on remote device; port 5900 is open so not sure what is the reason for this error. Can someone help please? What should I look for?

I contated HMI vendor (Maple Systems) and was told is Real VNC issue ...