Tony at the bottom of the menu, do you not see the little script icon like in the screen shot that Neilo posted?
Clicking the script icon should trigger the edit buttons in the property inspector.
The only thing i can see in your page code that may pose an issue is that the menu is inside a list, Try using a div instead of a list as the menu container.
if you still having an issue, it could be something with the way the site is set up. In the Dreamweaver site, is the page at the root o the site? Is the CSSMenuWriter folder at the root of the site?
Can you post screen shots showing your site settings, especial the local files path.
Also, what is your version of Dreamweaver and what is your OS?