If you have a vBulletin powered forum, one of the things you should do to make it easy for people to follow what is going on in the forum is to activate your forum's RSS Feeds subscription url. By default its disabled in new vBulletin install. The simple steps below will get your rss feeds url working.

Once loggged into you control panel, navigate to the options below and set them all to Yes

Admin CP -> vBulletin Options -> External Data Provider ->
Enable External Javascript
Enable RSS Syndication
Enable XML Syndication