Very possible that the gas line has gotten air into it over the winter.
Suggest you get a butane lighter and hold it next to the burner, and let it run until it lights. It could take a minute or two until you get propane to the burner.
Once you've got propane to the burner, it should light normally.
Note that if this is the problem, you may also have to try to light off the water heater and furnace a few times until the gas gets through the lines to them, too. (Unfortunately, you can't use a butane lighter on those!)
UPDATE - It goes without saying that you should also make sure the gas is turned on at the tanks. Your propane regulator may also have locked up. See post #14 here about resetting it:
Aux propane tank kit.