Problem filling 5 gal LP tank - help please

I am a certified Propane filler. The probable problem is that the float on the OPD valve is stuck. This can occur if the tank has no liquid in it and that the operator opened the valve too rapidly at the beginning of the filling process...this many times happens on the first fill whether the tank has been purged or not. Since propane boils to a gas at -60 degrees F, as soon as the liquid hits the bottom of the tank there is a huge force of gas upward. The float can be violently thrown up, get stuck and can even be damaged. It has been suggested that you drop the tank. This is good advise but turn it upside down and drop it on the top. The second solution if there is a gas lock is to have the filler connect the tank to their purging device and release pressure on the OPD valve. If neither of these work the tank's OPD valve has probably been damaged.