This item was voluntarily recalled by LEGO Systems on July 21, 2009 in cooperation with the US Consumer Products Safety Commission after it was determined that the batteries could overheat inside some of the units sold, posing a burn hazard.
The units in question were originally sold between April 8 and May 6, 2009 directly through LEGO Shop at Home. A small fraction of these units were found to overheat because of defective placement of a metal battery terminal contact. Most of the over 1600 units sold during this period are fine-- if the unit does not overheat when turned on it does not have the defect and is safe to operate. All units originally sold by LEGO Systems after May 6, 2009 are not a part of this recall.
Those who have a copy of this item that overheats when turned on should immediately stop using it and contact LEGO Systems for information on what to do.