server-side-includes

Why isn't #include working on .asp page in IIS7.5?

I saw a similar question to this, but mine is slightly different: I'm get intermittent results with #include files working on an IIS 7.5 server (R2008 V2). My includes are only working if they are in the same folder as the current .asp page, or in a subfolder of the current page. This is inconvenient, as I'd like to keep them all in a /...