Also, I had an issue with mine freezing around the valve on the tank too last year while riding with JohnG and Bob Youmans. I know they remember it, because it would barely run and I had to end up just going back to camp at Morris Mtn. I have not done one single thing to it, and have not had a single issue out of it since, by only cranking the valve a couple turns to turn the flow "on".... I used to turn it until it was all the way open, and that's when it would freeze up, by allowing too much flow like mentioned above in an earlier post.
Hope this helps, but I still think we need to know if you are running your bottles via liquid port or vapor port.