http://www.propanetankstore.com/blog/why-does-my-new-propane-tank-need-to-be-purged/

Since I am in the business of selling propane heaters, I know all too well
what happens when tanks are not properly purged. I've had several customers
with frozen regulator problems this season - all with one common cause: the
tanks were not purged prior to the first fill! It doesn't take much moisture
in a tank to cause this, and then I get the complaint because the expensive
heater is always suspected first, rather than the simple problem that
someone didn't feel it was necessary to follow directions!

Karl
propexusa.com