MIL code 455 Evap control system, gross leak

My 2002 Cabrio GLS, 121 CID engine, automatic trans. has been giving me a code 455 lately. The light comes on, goes off, comes on, etc. VW has seen the car a few times. A VW service trip likely precipitated this problem. I was having trouble filling the tank, the filling station nozzle would click off even though the tank was empty. VW fixed this problem somehow by taking something apart and putting it back together. That problem is solved, but now I get code 455.

Code 455 is a gross leak in the EVAP system, which I think can very easily be related to something VW reassembled improperly.

Has anybody else had this problem, or maybe have an idea. I'm going back to them with this complaint, but I'm wondering if anybody here has any thoughts.

Bill

[make sure the filler cap is on tight.
do you hear a hiss when you undo the filler cap when filling up? if so theres a prob with the tank venting system.
the gross leak fault lends me to think the vent pipe from the tank to the charcoal canister is open to atmosphere. or the activated charcoal filter valve is stuck in the open position(mechanically). this valve should click for about 30 secs after startup. does it?
is there a fuel odour in or near the car?