Dan Brown's books, while fascinating, are a lot of times inaccurate in the links Brown is trying to make.
I've just finished reading his latest work, The Lost Symbol, a week and half or so ago, and without doing a research on the internet I've managed to spot myself three inaccuracies.
For example, he has made the claim that Amen, the word used religiously by all three big religions, is derived from the name of the Egyptian God, Amun, while in truth, this is nothing but a baseless theory.
In reality the word is based on the Semitic language, specifically ancient Hebrew. It comes from the word 'emuna', which means faith, and Amen itself is supposed to mean "believe it and it will be so" or something like that.
Another example would be the etymology of the word sincerely, and Dan Brown has used this in his book The Digital Fortress as well as The Lost Symbol.
He claims there that it originally meant "without wax" (Sine = without, cera = wax) while again this is nothing but a theory, in truth it comes from Latin Sincerus which simply means "pure" or "clean", and is believed to literally mean "one growth" (Sin = one, crescere = to grow).
However, of course he does make many accurate links such as the claim that the word "cereal" is being derived from the name of Ceres, the Roman Goddess of agriculture, and many other claims.