What he said.
There is a safety valve on all new tanks. It's supposed to sense a failure
like a blown hose and shut off or shut nearly off.
Occasionally a tank will activate the safety valve when it is first
opened and is trying to pressurize your system.
The fix is to shut off all gas appliances and shut the tank and wait a second
or 2 and then slowly open the valve.
You might unstick a stubborn safety valve by tapping the tank
with a hammer handle or bump it with a piece of fire wood.
Just a good tap should do it.
Sometimes I think if they make things any safer we'll not be able to use them!