Our C3 Picasso VTR+ has recently come up with the following waring display;

Anti Pollution Fault. The first time it appeared there was no problems and re-set itself. However, the same message came up today and the car seemed to lose all power. After a f 15 minute stop all seemed okay but engine management warning light stayed on. After about 5 hours the warning light reset itself. Has any one eles experineced this fault, and what is the cause/cure etc.