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Click HERE for the service manual for your furnace. I am assuming you have the pilot model, so look at section D for the lighting instructions.
It is not totally clear if you are having problems lighting the pilot, or if you can't get the main burner to light, although I am assuming that you are trying to light the pilot.
Are your other propane appliances working properly? Please note that it is very important to have your propane system inspected annually for leaks, proper pressure, and overall condition.
At any rate, the service manual should help address your problem. If not, please let me know and I can try to assist you further.