@himbeerschaaf
System Default Http Proxy.
It says it truies to use a proxy to connect to the internet and fails there.
check your web browser proxy settigs and the windows proxy settings and disable any proxy that is entered there if you are sure you would normally not use any proxy.
A proxy is redirecting the data to some other IP to "normall" ease the loading of websites (from a cache e.g.) but it also could be that some malware has installed a proxy to reroute the internet traffic to other sites so they are able to spy you!
So check your system for any proxy enabled and disable it.
Else:
Did you try point 13. from the troubleshooting guide
https://www.esoui.com/forums/showthread.php?t=8082
already as it often is the cause of that problem!