[wafriend]

I finally figured it out, the relative path should be set to /v3b/forums/. I needed to add the trailing slash, something not mentioned in the documentation and not reflected in the example to the right of the field.

By the way, your documentation isn't current with version 2.6.3 of Wordpress. The settings menu is no longer "options" it is now settings. It is also "vbridge settings" and not "vbridge options"