Mith-
Because I copy/pasted a PM sent to me, some things in the previous post might be a bit unclear.
This portion was the commentary from a PM:
"Traditionally, theologians before Vatican II, and those whom the Society has cited in defense of its position have always said we may resist non-infallible acts and teaching under some circuмstances, ordinary magisterium that is merely "authentic". In this article, the Society expressly teaches that it is impossible that God allow errors in something the Pope declares infallibly."
The rest was a quote the PM'er supplied from the work of Dom Paul Nau:
"The Almost Total Eclipse of the "Authentic" Magisterium
The Church's current crisis is not at the level of the Extraordinary or Ordinary Infallible Magisterium. This would be simply impossible.
Normal Times and Abnormal Times
Dom Nau makes it clear that this prudential assent does not apply in the case of a teaching that is "already traditional," which would belong to the sphere of the Ordinary Infallible Magisterium. However, in the case of a teaching which is not "already traditional," the reservation which interests us does apply: "unless the doctrine rejected...involved a manifest discordance between the pontifical affirmation and the doctrine which had hitherto been taught." Such a situation would legitimize the doctrine's rejection and would imply no "mark of temerity."
This is not a case which can be excluded a priori since it does not concern a formal definition. But, as Bossuet himself says, "It is so extraordinary that it does not happen more than twice or thrice in a thousand years" (Pope or Church? p.29).
In such a case, refusing one's assent does not only not manifest temerity: it is a positive duty. The "discordance" with "doctrine which had hitherto been taught" dispenses the Catholic from all obligation to obedience on this point:
The general principle is that one owes obedience to the orders of a superior unless, in a particular case, the order appears manifestly unjust. Similarly, a Catholic is bound to adhere interiorly to the teachings of legitimate authority until it becomes evident to him that a particular assertion is erroneous (DTC, vol.III, col.1110)."
http://www.sspxasia.com/Docuмents/SiSiNoNo/2002_January/Popes_Infallible_Magisterium.htm