Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Here is a refusal with a different flavor. Your arguments were fine. Every type checked out, the wiring was in place, and the builtin actually started running. And then the builtin itself said no and returned a code. That is what this message reports. It matters because it is not the same as a type error, where the value was the wrong kind, and it is not a wiring error, where the function could not be found. Here, the call was perfectly lawful on paper, and the builtin made its own judgment while doing the work. Think of handing a valid ticket to a train conductor: the ticket is genuine, the train exists, and he still says this seat is taken. The message names the builtin and the code it returned. That code is your lead. It tells you what the implementation objected to, such as a missing file or a value out of its working range. These are kept as a separate refusal so that when you read a log you can tell at a glance which of the three situations you are in. Look up the code for that builtin, adjust the call or the situation around it, and run again.
Text from the Rush engine's error catalogue.