Trait implementations can only implement associated types that are members of the trait in question. This error indicates that you attempted to implement an associated type whose name does not match the name of any associated type in the trait.

Erroneous code example:

trait Foo {}

impl Foo for i32 {
    type Bar = bool;
}

The solution to this problem is to remove the extraneous associated type:

trait Foo {}

impl Foo for i32 {}