According to Dei Verbum Sacred Scripture is infallible.
Sacred Tradition is infallible because it is the deeds of the Infallible and Most Holy Trinity. Everything that God is and everything that God does is One Divine Eternal Infallible Act. Sacred Tradition is infallible because it is a true reflection and a true work of the Infallible Father.
If the deeds wrought by God in salvation history were merely teaching stories or myths, with little or no historical value, then Tradition would cease to be the deeds of the God and would not be infallible.
3. Sacred Scripture proceeds from Sacred Tradition.
Sacred Scripture is infallible because it proceeds from infallible Sacred Tradition. Sacred Scripture is infallible because it is a true reflection and a true work of the Infallible Son. Sacred Scripture is infallible because it is words written by God, and because it is the Word of God, and because it is One Utterance of God.
Catholic Planet (They're out of this world)
As I've said before, the non-apostolic folks make up their own wrong interpretation not only of the Bible but any and all other things.
The dei verbum says
His goodness and wisdom God chose to reveal Himself and to make known to us the hidden purpose of His will (see Eph. 1:9) by which through Christ, the Word made flesh, man might in the Holy Spirit have access to the Father and come to share in the divine nature (see Eph. 2:18; 2 Peter 1:4). Through this revelation, therefore, the invisible God (see Col. 1;15, 1 Tim. 1:17) out of the abundance of His love speaks to men as friends (see Ex. 33:11; John 15:14-15) and lives among them (see Bar. 3:38), so that He may invite and take them into fellowship with Himself. This plan of revelation is realized by deeds and words having in inner unity: the deeds wrought by God in the history of salvation manifest and confirm the teaching and realities signified by the words, while the words proclaim the deeds and clarify the mystery contained in them. By this revelation then, the deepest truth about God and the salvation of man shines out for our sake in Christ, who is both the mediator and the fullness of all revelation.
I think it depends upon whether the meaning of "infallible" is restricted to men definitively proclaiming a doctrine of faith or morals, or being a source incapable of deceiving or being in error. And of course, RCs (as well as Prots) debate the precise meaning of inerrancy.
The issue of whether Scripture is infallible has been inconclusively debated much on Catholic forums, as I know of no "official" (that also being an issue of some debate) teachings that explicitly states that Scripture is infallible or is not infallible, though i think papal affirmations of it weigh stronger in the direction of infallibility.
I think the assertions by RCs that Scripture is not infallible are often driven by the desire to elevate the authority of the Roman magisterium above Scripture, which in fact, it effectively presumes even though it comes short of claiming Divine inspiration.
As the Catholic Encyclopedia states,
Inspiration signifies a special positive Divine influence and assistance by reason of which the human agent is not merely preserved from liability to error but is so guided and controlled that what he says or writes is truly the word of God, that God Himself is the principal author of the inspired utterance;
but infallibility merely implies exemption from liability to error. God is not the author of a merely infallible, as He is of an inspired, utterance; the former remains a merely human document. http://www.newadvent.org/cathen/07790a.htm
However, this definition does not leave Scripture to be less than infallible unless one holds that it is liable to teach error, while it claims infallibility for a human document lacking Divine inspiration (but not protection) in contrast to Peter's confession and the rest of Scripture.
A Catholic poster who argues on "Catholic answers" forum (http://forums.catholic.com/showpost.php?p=3614383&postcount=1) for Scripture being infallible sees denying infallibility to Scripture as being based on faulty logic and "uncharitable, especially given the number of times that This Rock has used the word infallible in exactly the same way." as,
This Rock has used infallible to describe decrees, statements, definitions, dogmas, documents, doctrines, professions of faith, teachings, catechisms, canonization, Sacred Tradition, the Apostles Creed, the Nicene Creed, the Athanasian Creed, and even the Summa Theologiae of St. Thomas Aquinas.
I think the reason some RCs teach that Scripture is infallible is because they see it as impossible for it not to be so if God is the author of it, (CCC 105) and "the books of Scripture firmly, faithfully, and without error teach that truth which God, for the sake of our salvation, wished to see confided to the Sacred Scriptures," (CCC 107) and is otherwise stated by their church to be inerrant.
And as said, the premise of some that it cannot be infallible because it can be misunderstood is also true of the Magisterium, which has infallibly declared that it is (conditionally) infallible.
And the authority which the RC's claim gives the RCC their claim to infallibile Sacred Tradition, is what again?
Isn't it the Scripture they claim to have written and appeal to for their authority?
Or are we to accept their claim of infallibility and Sacred Tradition on their say so?
Circular reasoning much?