Chuck; an LP regulator is designed to be heated by using coolant from the engine. You must have coolant flow from the cooling system to the LP regulator. Any restriction in flow could cause the LP regulator to freeze. Some of the basic things to check would be.
1. Proper engine coontant level
2. Coolant flow from the water pump to the LP regulator back to the engine.
3. There might be an air lock in the coolant hose or the LP regulator.
4. There may also be an air lock inside the LP regulator.
5. In order to clear the system of this potenial air lock; slightly open the coolant hoses to and from the LP regulator until all the air is released. Be careful the fluid may be hot.
I may have missed a few items but this would be the basic's for this kind of problem. If you have an engine overheating problem along with the LP regulator freeze you may have a worn water pump or restricted radiator causing reduced flow to the engine and LP regulator.