Apparently the problem was big. Really big. According to The Age and The Herald-Sun, thousands of cases were at risk of dismissal because of this problem.
Today, the Government rushed through emergency legislation, passing the Evidence (Miscellaneous Provisions) Amendment (Affidavits) Act 2012 in the Legislative Assembly. The Act isn't yet online — it has to pass the Legislative Council, which is sitting on 29 Feb, and receive Royal Assent — but the Bill is available here.
It will amend the Evidence (Miscellaneous Provisions) Act 1958, inserting two new sections.
Section 165 attempts to remedy the problems created with affidavits that weren't sworn.
165 Validation of certain acts and documents
(1) If an affidavit signed before 12 November 2011 by a person and by a person duly authorised to administer oaths contains words indicating that the first person states that the affidavit is made on oath or affirmation—
(a) it is not, and was not at any time, necessary that—
(i) the oath or affirmation be made orally; or
(ii) the first person signed the affidavit in the presence of the person duly authorised to administer oaths; or
(iii) the person duly authorised to administer oaths signed the affidavit in the presence of the first person; or
(iv) if the first person signed the affidavit in the presence of a person duly authorised to administer oaths, the person so authorised observed the person signing the affidavit; or
(v) the affidavit contained the statement required by section 126; and
(b) the words indicating that the first person states that the affidavit was made on oath or affirmation are and are taken always to have been effective by way of oath or affirmation even if anything referred to in paragraph (a)(i) to (v) was not done or did not occur.
(2) A warrant, an order, a summons or other process issued or made by a court or a judicial officer in reliance, directly or indirectly, on an affidavit referred to in subsection (1) is not invalid only by reason of the fact that, but for subsection (1), the affidavit would not have been duly sworn or affirmed.
(3) For the purposes of the prosecution of an alleged offence, the fact that, but for subsection (1), an affidavit would not have been duly sworn or affirmed is to be disregarded in determining whether evidence obtained in reliance, directly or indirectly, on that affidavit ought to be admitted.
(4) Subject to subsection (3), this section does not limit a discretion of a court—
(a) to exclude evidence in a criminal proceeding; or
(b) to stay a criminal proceeding in the interests of justice.
(5) This section does not affect the rights of the parties in—
(a) the proceedings known as Director of Public Prosecutions (Vic.) v. Marijancevic (No. 264 of 2011), Director of Public Prosecutions (Vic.) v. Preece (No. 263 of 2011) and Director of Public Prosecutions (Vic.) v. Preece (No. 265 of 2011) in the Supreme Court of Victoria, Court of Appeal; or
(b) any other proceeding in which a court, before the day on which the Evidence (Miscellaneous Provisions) Amendment (Affidavits) Act 2012 receives the Royal Assent, has made a ruling on the validity of—
(i) an affidavit referred to in subsection (1); or
(ii) a warrant, an order, a summons or a process issued or made in reliance, directly or indirectly, on an affidavit referred to in subsection (1); or
(c) any other proceeding in which a court, before the day on which the Evidence (Miscellaneous Provisions) Amendment (Affidavits) Act 2012 receives the Royal Assent, has made a ruling on the admissibility of evidence obtained under a warrant, an order, a summons or other process issued or made in reliance, directly or indirectly, on an affidavit that, but for subsection (1), would not have been duly sworn or affirmed.
(6) In this section affidavit includes a document purporting to be an affidavit.
This section seems to cover everything that might make an affidavit deficient, aside from the mention of the absence of the use of a holy book for swearing an affidavit. Section 103 of the Evidence (Miscellaneous Provisions) Act 1958 provides that there is no need to actually use a religious text when making on oath. (Or to even have any religious beliefs!)
Section 126B creates an offence for purportedly swearing an affidavit.
126B Miscellaneous False or misleading statement as to swearing etc. of affidavit
(1) Subject to subsection (2), a person must not make a false or misleading statement as to—
(a) the circumstances in which an affidavit or a document purporting to be an affidavit was sworn or affirmed; or
(b) whether or not an affidavit or a document purporting to be an affidavit was sworn or affirmed—
knowing that the statement is false or misleading.
Penalty: 10 penalty units.
(2) This section applies—
(a) only in relation to a statement made on or after the commencement of section 4 of the Evidence (Miscellaneous Provisions) Amendment (Affidavits) Act 2012; and
(b) whether the affidavit or the document purporting to be an affidavit was sworn or affirmed before, on or after that commencement.