Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You wrote a quoted text in a place that expects a name, and the engine asked you to remove the quotes. Some builtin arguments are name sites: the first argument of append, for example. A name site accepts a bare name. And for a door that can also follow a file, it accepts a bare path. So append, slash tmp slash a dot txt, comma v, is fine, with no quotes. But if you write that path in quotes, it becomes a text, and a text is not a file. A name is never quoted. In the past, the engine answered this with a confusing message, saying it did not parse a construct, and even quoted your text back as if the text were the problem. That blamed the parser for something it had read perfectly. Now the refusal has its own id, shows the quoted text, and offers both lawful spellings, the bare name or the bare path. The fix: remove the quotes. Then the engine knows you mean a real holder or a real file.
Text from the Rush engine's error catalogue.