2004 Toyota Camry CHECK ENGINE LIGHT AND CATALYTIC CONVERTE

In 3/2007 my Toyota Dealership informed me that the "check-engine" light was due to the catalytic converter needing to be replaced (they made several smaller repairs that did not fix the light prior to this repair). They did replace the CAT underwarranty in 3/07. In November of this year (20 months later) the check engine light returned and the same dealership is saying again that it is the CAT that needs to be replaced - this time it is not under warranty and the initial part in 2007 apparently only has a 1 year guarantee.

Does it make sense that a car with less than 100,000 miles would need this repair twice in less than two years, and if so, would this indicate a much larger engine problem. I am trying to determine how long to fight them on this (the repair is $861).