To be able to edit the user registration solution pack files in Dreamweaver, they must be at the root of your Dreamweaver site.
from your description of the problem it sounds like the user registration files are in a sub directory of the Dreamweaver site.
Change the Site definition so that the User registration files are at the root of the Dreamweaver Site.
NOTE: do not confuse the term "Dreamweaver Site" with your actual site. I am referring to the site as defined inside pf Dreamweaver.