Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your manifest declares a database, but the declaration is not written the way rush expects. Let's look at the correct form. In the config call, you list your databases as maps. Each one has a name, and optionally a path. For example, a database called clients with a path to its file, and another called products with no path. You may also pick the project's single engine, sulfur or sql. If you pick nothing, it is sulfur. Now, what does rush refuse? A database with no name. The same name written twice. A name with capitals or dashes, since only lowercase letters, digits and underscores are allowed. A path on the database called default, because nothing moves that file. An engine word other than sulfur or sql. Or the engine declared twice. The whole declaration is refused at once, before any source file is parsed, so you never run on half a configuration. Read the message, find which rule your declaration broke, fix that line, and load again.
Text from the Rush engine's error catalogue.