Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your node could not open a network connection, and the message tells you where it stopped. Let's go through the causes. The commands rush node serve and rush node dial talk to the network only through the engine's I/O door. A refusal can come from the kernel itself, for instance an address already in use, a port that is not allowed, or a peer that is not listening, and the second slot shows the system error. It can also come from how you wrote the address. The host must be a numeric IP address, version four or six, because this engine does not consult a name resolver at that step. The endpoint must look like an IP, a colon, and a port, with square brackets around IPv six. And if you pass a node ID instead, it must be in the Namewise roster, with an endpoint listed. Say you typed a host name, like example dot com. Replace it with its numeric address. Check the spelling, the roster, and whether the peer is up, and dial again.
Text from the Rush engine's error catalogue.