Looks like that server is supposed to be working but it does appear to be under heavy load so it may have intermittent problems with receiving completed WU's.
If you go to http://18.104.22.168
and the page displays as OK then you should have good connectivity. Just make sure you don't have a firewall or other data network security mechanism in place that is blocking the GPU client but based on the error messages you posted I don't think that is the case.
Your GPU client will continue trying to transmit the completed WU's while it's running. So as long as it successfully transmits within 48 hours of downloading the WU then you'll get credit for it. If it goes longer than 48 hours though then it's not credited.