Undecided If you get an "Io exception: The Network Adapter could not establish the connection" error try if the DNS works correctly.
In my case a nslookup to the host-adress NSLOOKUP TESTSERVER was possible and returned the IP-adress.
But in the other direction it did not work NSLOOKUP 123.123.123.123 the problem was a misconfiguration on one of our DNS-Server.