You attempted to use instanceof to determine if an object was derived from a particular function class, but you redefined the object's prototype property as either null, or an external object type (both not valid JScript objects). An external object can be an object from the host object model (for example, Internet Explorer's document or window object), or an external COM object.
To correct this error
-
Ensure the function's prototype property refers to a valid JScript object.
See Also
