HubPages changed its publishing standards back in April 2011 such that affiliate links are no longer allowed. Here's an excerpt from their blog:
"Affiliate Links: We no longer allow Hubs to link (directly or through redirects) to affiliate or commerce sites which are prohibited under the HubPages rules (e.g. Clickbank and sites that sell eBooks, promote dubious offers, contain a lead capture form, redirect users to unwanted websites, or contain pop-ups, pop-unders, or other features that interfere with sight navigation)."
Here's a link to the full article:
The sanctioned affiliate programs are Amazon, Google Adsense, the HubPages Ad Program, and eBay (coming soon). I use the first three and will probably start using the eBay program when it's available. Hope this helps.