Old URLs referencing forum IDs that are no longer valid. The current "Vendors Section" forum was the old "General Sportbikes" forum, based on an number defined, determined by the order in which the forums were created. General Sportbikes used to be "Forum #3", now it's "Forum #5". The "Vendors Section" just so happens to be "Forum #3" now.
Fred just hasn't updated all the URLs on the index page. You're bound to find more examples of "outdated links" as you poke around.