Error COBCH1728 ("type-name1 does not have public implementation of method method-name of interface type-name2") is also produced with this error.
In the following example, this error is returned for System.Windows.Forms.Control:
$set ilref"System.Windows.Forms" class-id MainView inherits type System.Windows.Forms.Form implements type IMainView. end class. interface-id IMainView public. method-id Show. end method. end interface.