Factual error: The Book of Mirrors is a rare medieval manuscript, yet Casey has no problem whatsoever in bringing the book to Rabbi Sendak. No library would lease such a valuable item and stealing it would also be rather difficult, as you are supposed to deposit a document and fill out a request form before you are permitted to consult any similar manuscript in any European or American library (if you are allowed at all to do so without a research permit).
Factual error: In the part where the two girls are chatting using Apple's iChat, which is another form of AIM, they are using a service supported by Apple called Bonjour. Bonjour is a network discovery technology developed by Apple, Inc. It allows computers and printers to automatically find and connect to each other's services using a new communication protocol, saving time and simplifying tasks such as file sharing and setting up printers. This would mean the girls would have to be very close to each other to use it, and obviously they weren't.