It seems that the archives have been taken down because of "legal issues related to the ownership of the content." See http://publishing.mathforge.org/discussion/169/clockss-and-portico/#Item_18 for further discussion. Unfortunately, nobody involved seems to be publicly discussing the situation, and I have not yet been able to learn exactly what's going on. One natural guess is that this has something to do with how the journal ended, but I really don't know. In any case, it's outrageous for a journal to disappear, and the community deserves to know why it has happened and what can be done about it.