I insert a short quote below. For a detailed refutation of Pagel's scholarship, I advise anyone to read the article, which is not too long.
"Put simply, Irenaeus did not write what Prof. Pagels wished he would have written, so she made good the defect by silently changing the text. Creativity, when applied to one's sources, is not a compliment. She is a very naughty historian.
Or she would be, were she judged by the conventional canons of scholarship. At the post-graduate institute where I teach, and at any university with which I am familiar, for a professor or a grad student intentionally to falsify a source is a career-ending offense. Among professional scholars, witness tampering is no joke: once the charge is proven, the miscreant is dismissed from the guild and not re-admitted.
The Gnostic Gospels, like those portions of Pagels's later work with which I am familiar, is chock-full of tendentious readings and instances where counter-evidence is suppressed. The example of "creativity" here discussed may fairly be called a representative specimen of her methodology, and was singled out not because it's the worst example of its kind but because it's among the most unambiguous. No one who consults the source texts could give Pagels a pass, and that means she forfeits the claim to reliability as a scholar. Attractive as her ideological sympathies may be to many persons -- including many academics -- she does not deserve to be ranked with serious textual scholars ... and her testimony on the accuracy of inventions such as Dan Brown's The Da Vinci Code cannot be solicited without irony."
http://www.cwnews.com/news/viewstory.cfm?recnum=43736