Disappearing links may occur for one of the two following reasons.
First, Kontera is constantly creating and building relationships with advertisers. These ad campaigns sometimes have expiration dates. Every time a user rolls over one of our ContentLinks, our java script sends a call to our server in order to bring back the highest paying ad. Sometimes when a call is sent to our server, it is expecting to pull an ad from a previous campaign that may no longer have money left to spend, or has met it's quota of impressions. This is a valuable feature, it shows that our algorithm is aiming to pull the highest paying words possible for our Publishers.

A second reason that the ContentLink might disappear is because the algorithm found a better word to link, that is; it finds a more relevant keyword or a keyord that pays more per click.