[edramshaw]

You are probably missing the washer that goes between the beer line and the coupler. Untap the keg, turn off the gas and undo the hex nut that attaches the beer line to the coupler (the things that goes into the keg). There should be a black washer in there, if not you've found the source of your leak. If not check the other ones as well, with what you describe I wouldn't be surprised if it was the washer on the gas side of the coupler. You can find replacement washers at Micromatic for a buck or so. Good luck!