Code PO449

Hi i have a 99 van and the engine light came on the other day, I found the code to be PO449. This code has to do with "evaporative emission control vent/solenoid control circuit malfunction".

My question is what is this and where is it, finally how do i fix it?

Thanks

it could be a complex problem or is just your gas cap isn't tight or your refuel while it was running