When going to Window > Extensions > Generate Google Sitemap, filling out Site URL and Homepage, then clicking Auto Discover, I get a popup:

Dreamweaver
Access to [site root directory/subdirectory] was denied.

Clicking OK gives me:

While executing timer in dmxGoogleSitemapProgress.htm, the following JavaScript error(s) occurred:
...
...
...\dmxGoogleSitemap_lib.js":
getDocumentDOM: Argument number 1 is invalid.

I've tried reinstalling DMX extension and clearing Dreamweaver cache, but same error. I've also confirmed that the System has Read permissions on this folder.