Sometimes moisture can get into things, even with the propane tank under pressure (The moisture may have gotten back at the Refinery) and the regulator can freeze.
Another possibility is the gas in the tank,, There are two gasses that all summer long work nearly identically. Propane and Butane, in fact you get a few (not many) more BTUs from Butane. And Butane is cheaper.
So some propane dealers, epically in areas where it does not often freeze, will substitute BUTANE for Propane, charging the higher Propane price, and pocketing the extra profit.
Yes this is fraud.
So, I said "All SMMER long. But what happens in the Winter?
Well, In the winter it gets cold outside, and if it gets down to oh, say 30 below the person with PROPANE stays warm and cozy.. (in fact the boiling point is closer to -40)
But the poor person with BUTANE in the tank... Well, He is in trouble at around 30 ABOVE.. Yes, it will not boil, (Vaporize) at about the freezing point of water.
So if your tank is full of Butane, nothing to ignight.
Finally there are several things that can go wrong.
For example my furnace did light, but almost immediently it shut off the gas,, Then it tried again, and again.
The result.. A new control board,,, but I checked a whole raft of other things first. I have posted the list (Chart) elsewhere. Ask if you need it again.