Carbon Molecules

Looks like we have an answer.

"The problem is, as NASA's Douglas Ming (the Merciless) has pointed out in a recent paper, the experiments to search for carbon involve heating soil samples to a few hundred degrees and sniffing the vapours. If the soil contains carbon molecules and perchlorates, the carbon molecules will simply burn up. No wonder they couldn’t find any."

Fred

http://timesonline.typepad.com/science/2009/06/is-there-a-mars-conspiracy.html

Interesting article and it does not surprise me in the least, missions always seem to be in search of conditions that could or could have supported life on Mars rather than looking for life itself.