WTOS thin clients refusing remote login after connecting to ftp server.

Event log error: "Signon server (http://ServerName) is not responding"

I have checked the following:-

-DHCP option 161 pointing to IP

-Everything pings back (Host server, VM, & thin clients)

-Published desktop collection accessible from browser -Self-signed SSL certificate added to thin client using wnos.ini

-ISS ftp & default web sites bindings to firewall ports 21, 443 & 80 opened

The thin clients are Wyse S10 Version 6.3.0_12

All RDS roles installed on a single server (ServerName), with DC on VM, all on Server 2012 R2