There are some paths and page names that DWiki categorically refuses to serve, even if they seem to resolve to real files. Because they're enforced by both low-level code and high-level code, they apply to DWiki pages, static files being served by DWiki, and even templates. (Technically they apply to comments too, but comments can't generate file names that violate these rules.)
Any path that includes a path component that starts with a ., ends
with ,v or a ~, or is RCS.
Any non-relative path that includes .., ., or a sequence //;
usually this might appear in the URL of an incoming request. (Incoming
requests are not supposed to include things like that. But
ChrisSiebenmann declines to believe that everyone sending DWiki
requests is going to do what they're supposed to.)
DWiki will reject REDIRECT files that either have too many '..' entries (so that they are trying to escape the root of the page directory) or that fail these checks after they've potentially been converted from relative path names to absolute inside-DWiki paths.
When DWiki rejects bad paths, generally it says that there is no page by that name. Sometimes it rejects the request entirely in huge flames.