Thrown when a MechanicFactory is considering whether or not to produce a Mechanic and finds that an area of the
world looks like it it was intended
to be a mechanism, but it is is some way not a valid construction. (For example,
an area with a "[Bridge]" sign which has blocks of an
inappropriate material, or a sign facing an invalid direction, etc.) It is appropriate to extend this exception to
produce more specific types.