Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your script tried to read a file, and there is no file with that name. Let's talk about how rush answers that. Some languages would return null, or an empty text, and let the script go on. Rush does not. If you search for a file and find none, the honest answer is the good old one: no such file or directory. Why not null? Because null looks like a value, and an empty text looks like an empty file. And an existing empty file really does read as an empty text. If rush used the same answer for a missing file, you could never tell them apart. So the read refuses. A try block can catch it, and a script without one stops right here. The first slot names the path that was asked for. A typo in the folder name is the most common cause, so check the path first. And if the file may or may not be there, ask first with exists, and decide what to do on each branch. A missing file is a fact, not a surprise.
Text from the Rush engine's error catalogue.