The connection was reset.
Check your internet connection.
Check any cables and reboot any routers, modems, or other network devices you may be using.
Allow Opera to access the network in your firewall or antivirus settings.
If it is already listed as a program allowed to access the network, try removing it from the list and adding it again.
If you use a proxy server…
Check your proxy settings or contact your network administrator to make sure the proxy server is working. If you don't believe you should be using a proxy server: Go to the Main menu > Settings > Change Proxy Settings… > LAN Settings and deselect "Use a proxy server for your LAN".