Did you check to make sure you don't have any collapsed or kinked vent lines?
If the lines are are OK, I would agree checking the lines for charcoal pellets (from the old canister) getting up into the lines and plugging them up might be worth checking. A few guys have gone through this and know the ideal pressure to use when blowing the lines out to clear them. Hopefully one of them will see your thread and drop in to opine.
Oh and if you get them cleared, don't add anymore gas after it kicks off when it is full.