Well,
At the site, everything works fine. With the laptop connected to the network switch, launched RsView client, home screen comes up and no error.
At home, I had similar error to yours when my laptop was connected to the network through the RADES-9300 modem. I launched the RsView client and it said something like "Cannot connect to HMI Server". What was weird was that I can ping the HMI server computer, the PLCs, and go online with the PLC, but received the error when I launched RsView Client.
Once I added the HMI server computer to the laptop's host file, everything works fine. I can launch RsView client, can see the screens and no more error.