MethodInstance with Name '{0}' on Entity (External Content Type) with Name '{1}' in Namespace '{2}' of type '{3}' is missing ...

MethodInstance with Name '{0}' on Entity (External Content Type) with Name '{1}' in Namespace '{2}' of type '{3}' is missing a Property of Name '{4}' and type 'System.String' (or the Property value is empty). This Property qualifies the contents of the stream returned when the MethodInstance is executed.