I tried to access the URL through MWG and access is working fine. The error message is pretty generic and simply means that MWG was not able to talk to the web server. It could be a network problem (firewall issue), a DNS related issue, a configuration issue within MWG (wrong next hop proxy, ...), etc.
If you don't have knowledge of the MWG product but network knowledge and know how to troubleshoot networking related problems I recommend to start a packet capture (tcpdump) on MWG and try again. Then look at the packet capture and see if DNS resolved correctly and MWG is able to talk to the remote server.
Otherwise I recommend to file an SR with support.
Thanks Andre, I will pass this info on.