Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
A node showed up with a different key from the one rush remembers, and rush did not accept it. Here is the idea, familiar from SSH. The first time two nodes complete a handshake, rush pins the peer's key in a file. That is trust on first use. From then on, the same node must always prove itself with that same key. If a later handshake presents another key, either the node was legitimately re-keyed, or someone is pretending to be it. Rush cannot tell which, so it refuses, by name, and it never overwrites the pin on its own. If you started the conversation, you stop at the second message, and your Hello never leaves your machine. If you answer the call, you close the session. To re-key a node on purpose, Namewise removes its pin, and the next handshake pins the new key. The message shows the node and the mismatch. If you did not change any key, treat this as a warning, and do not connect until you know why.
Text from the Rush engine's error catalogue.