On Windows (any version probably) with the php isapi plugin the userewrite=2 (internal) doesn't work.
With the keyword Problem the generated Url will be:
http://localhost/wiki/doku.php/Problem
IIS will report 404 Not Found, because this Url is not mapped on /doku.php
A suggested solution is to introduce a new rewrite mode 3 (internal-iis) that will work with the following Url:
http://localhost/wiki/doku.php?Problem
or even better
http://localhost/wiki/?Problem