Adding to the above...
The url, https://www.guitartricks.com/songs/riffs does indeed take one to a list of Famous Riffs; fifteen of 'em by Anders. Unfortunately, only one of the fifteen works, Let It Be. Clicking on the others gets the same result as you. Further, despite the list at that url, the songs/riffs are seemingly no longer in Anders catalog nor does Anders' riff lessons show up in a search of Songs.
Perhaps they have been removed.
edited
"It takes a lot of devotion and work, or maybe I should say play, because if you love it, that's what it amounts to. I haven't found any shortcuts, and I've been looking for a long time."
-- Chet Atkins
-- Chet Atkins
