The link address contains "prev" which indicates that the address is relative to some other (prior) document. The reference to "cookie" in the error message indicates that the other (prior) document is supposed to be in a cookie on the user's computer. The bottom line is that these documents can only be accessed with the given links it it's done through the same script or page that created the links.
Bummer. :( I'm confused, though. I went back to the original PARIS home page for the site, and followed the hypertext trail all the way to the point where the doc numbers showed up; shouldn't that have provided me with the necessary "cookie," or am I just not grokking, here...?