Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You ran one of the wire test-vector commands, and one line of the vector file did not look right. Here is how those files work. Rush has commands that check its seal and its handshake against known test cases, called vectors. The file has one line per case. Each line starts with a verb and then holds fields written in hex, where a single dash means empty. Rush reads the file strictly. If a line uses a verb that is not declared, the run stops at that line. If it has too many or too few fields, same. If the key, the nonce, or the tag is the wrong width, same again. And for a handshake vector file, if one of its named fields is missing, the message names the missing field. Rush stops instead of skipping lines, because a test that quietly skips cases proves nothing. The first slot gives the file and the line number, and the second says what that line must contain. Open the file, go to the line, fix it, and run again.
Text from the Rush engine's error catalogue.