Does the NZB download to your default directory? If so, open it in Notepad or similar. If you see html rather than xml code, then your cookie info isn't confgured properly. To get the right cookie info, go to Newzbin page, log in and type in url box:
javascript:document.cookie
This should open a new page with active cookies that you can copy/paste. To get the fauth code, just navigate to a Newzbin RSS page and copy from the url.
-Hecks