anti pollutant faillure error

[scandiskwindows9x]

i have a Peugeot 307 Xline gasoline 1.6 engine TU5JP4 and started some days ago to warn me on the display anti pollutant error and the dashboard error light on , today the message disappeared but the light still on in the dashboard, i would send to the dealer to get the problem checked , but my question is what is the possibles causes of that message on display and the light of anti contamination system on in the dashboard?


any answer would be welcomed

best regards

Francisco