Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
The engine would not start, and the reason is a type nobody declared. Let me set the scene. Every builtin parameter says what type of value it accepts. That type must exist in a file called types.feml, along with a small rule that decides which values belong to it. This time, a builtin mentioned a type that is not in that file. So the parameter has a name for what it wants, but nothing that can actually judge a value. Imagine a bouncer told to let in only members of the club called Zebra, when no club called Zebra exists. He cannot check anyone, so the safest thing is to keep the door shut. The engine does the same: it refuses to be born rather than run with a parameter that judges nothing, because that would let wrong values slip through unchecked. The message names the type and the builtin that asked for it. You have two honest options. Fix the spelling if the type was meant to be one that exists, or declare the type: add a type group to types.feml with its name and the piece text that judges it. No C edits needed, just one declaration.
Text from the Rush engine's error catalogue.