What does “A server with the specified hostname could not be found” error mean?

In some cases, UPnP feature might be disabled by default on your router and you need to go to the router admin web page/console to enable it. In other less common cases, it might be possible that UPnP capability is not offered by the current router.

When this error happens, it means UPnP service cannot be found on the local network. The operation to create port forwarding on the router fails. This error often appears after the first compatibility test (i.e. searching for a router with UPnP service enabled) fails. 

The following articles explain potential workarounds that can solve this issue:

Enable UPnP on your router