Corrected entry: The book claims that early Christian texts which support the grail theory of "the Da Vinci Code", such as the Gospel According to Philip, were left out of the Bible because they prove the marriage between Christ and Mary Magdalene. These texts were in fact not included in the Bible, but the reason was that they were written after the 1st century and thus not as reliable. They certainly prove nothing of Christ's marriage, as a source from his own time saying that he was unmarried is far more credible than one dating more than 100 years after his death claiming that he was.
Corrected entry: The book claims that Jesus was named a deity rather than a prophet at a meeting in Nicaea in 325. Jesus is referred to as the Son of God and a divine person in the texts of the New Testament, texts which date much further back than 325. What was decided at the meeting in Nicaea was that Jesus was equal to God, and not a deity of "lesser rank".
Corrected entry: In the Da VInci Code, Opus Dei is depicted as a clandestine society of sinister monks. In reality, Opus Dei is an organization made up of lay people who lead rather ordinary lives. It contains very few priests and no monks at all.
Corrected entry: Prieuré de Sion (Priory of Sion) was founded in 1956. A bit hard for Da Vinci to be part of the group then, wouldn't you say?
Corrected entry: Walt Disney is pointed out as one of the members of the Priory of Sion, with references to the early Disney classics as proof that he knew the real truth of the grail and was a member of the group. Walt Disney died only a few years after the Priory was founded, and the early classics are older than the Priory. He could thus not have used his movies to spread the message of the group as the movies came first.
Corrected entry: When the guard at the Louvre is pointing the gun at Langdon, Sophie takes the 'canvas' painting of the "Madonna of the Rocks" off of the wall and uses it as a hostage - if the guard doesn't drop the gun she will supposedly tear the painting apart. However, the real painting has a solid wood back to it, making it too heavy to lift, let alone tear it apart.
Corrected entry: Langdon uses the name Amon L'isa to make an anagram that turns into Mona Lisa, a clue left behind by Da Vinci himself. The painting was never referred to as the Mona Lisa during Da Vinci's lifetime so it's impossible for the painter to use that name in any clue at all.
Corrected entry: The cylinder contains vinegar which will destroy the parchment if the two come in contact. Disregarding the fact that Langdon can simply put the cylinder in the freezer and get the parchment out safely that way, even if he broke it open it wouldn't be damaged. Vinegar does not dissolve parchment.