Lots can go wrong on the Mars side. E.g. Mars Polar Lander - smashed into Mars. Beagle 2 - last heard from just before landing. Mars Climate Orbiter - failed to land because of confusion between pounds and Newtons. Deep Space 2 - no communication after landing. Mars Observer - communication lost 3 days from Mars, probably due to fuel leak.
See "Mars Curse": http://en.wikipedia.org/wiki/Exploration_of_Mars#Probing_dif....