Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
A message frame on the wire was refused. Let's understand what a frame is. Rush talks to other nodes using Rush nine P frames, little packets with a checksum, a command, flags, a source and a destination. When one arrives, the codec checks every part, and the first slot of the message tells you which check failed. Frame checksum means the fingerprint did not match, so the frame was touched on the way. Command unknown or refused means the command is not declared, or is declared but not yet allowed, like migrate or leases. Flag unknown or refused covers flags like compression. Source and dest mean a malformed address. Short and trailing mean the frame had too few or too many bytes. Version means a version the engine does not speak. It can also be a file the I/O door could not read or write. The second slot names the exact command, flag, field or reason. Rush rejects the frame whole instead of guessing at its meaning. Picture a sealed envelope with a broken seal: you do not read the letter. Check the sender, the version and the transport, and send the frame again.
Text from the Rush engine's error catalogue.