gas leaking from canister after feuling up

hello
I have a 2001 maxima a couple of months ago when I put over a half a tank of gas it would come out of the canister.I bought the canister and evap valve at a junk yard and that seemed to fix it for a while but today when I was feuling up gas started coming out of the canister again and I am getting dtc p0446 which is the evap emiission control system vent circuit. any ideas what could be causing this?
Thank you
jason