Let me take you to a scenario.
Say, I am working on a project "test"
I created a book and 2 pages
in one page i wrote a line "click here to display chm help"
For that line, I gave a hyperlink "D:\Prateek\robo.chm"
Now, I tried to preview it, a windows download dialog appeared and then I downloaded the linked chm file & It worked fine.
Now I generated a Microsoft HTML(.chm) output and then clicked on "click here to display chm help". Now it opened a window and showed "Page not found".
I am using: Robohelp 10 in TCS4