E0017: Unknown Namespace

You referenced a namespace that hasn't been defined.

Example

fn main() {
    let s = Status::Active;  // Error: unknown namespace `Status`
}

How to fix

Define the namespace before using it. enum definitions are one way to create a namespace:

enum Status {
    Active,
    Inactive,
}

fn main() {
    let s = Status::Active;  // OK
}

Or check for typos in the enum name.