The unexplained disappearance of the previously- #OpenAccess Digital Einstein Papers is the subject of a question on the History of Science and Mathematics StackExchange [https://hsm.stackexchange.com/questions/18948/why-have-princeton-universitys-free-online-einstein-archives-disappeared], on which a bounty is now being offered for a definitive answer.
The comments on the question contain some speculations about the reason for the site being taken down. No answer has been offered yet, presumably because Princeton University Press, for all its publicity about the new paid-for database of the Einstein papers, seems to be quietly ignoring the 10+ years of open access that came before.
