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The reason the unit is shutting down is that it is not sensing flame. The burners need to light smoothly and immediately all the way across. Check for dirty or rusted burners, crossover slots (the slot on the burner that carries flame from one burner to the next) that are dirty, warped or not lined up properly. Finally, low gas pressure can also cause just one burner to light.
Have you tried bypassing the thermostat? It may be loosing a heat signal from the thermostat. Also, full model number would be much appreciated.