Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
A node introduced itself to another, and the introduction was refused. Here is how the introduction works. Right after the secure handshake, each side sends a short Hello, carried inside the encrypted channel. A Hello has a fixed size: the node's id, two hundred fifty-six bits, followed by a fresh authentication key, also two hundred fifty-six bits. Nothing more, nothing less. If a Hello arrives with any other length, the verdict is hello length, and rush rejects it, since a malformed introduction cannot be trusted. Two other problems are on this side of the wire. Hello node means this machine could not work out its own node segment. Hello entropy means the engine could not draw the fresh random key it needs. Each of those means the Hello could not even be written, and no one will be fooled by a half-made one. Check the length of what the peer sends, and make sure your machine has its identity and a healthy source of randomness. Then connect again.
Text from the Rush engine's error catalogue.