Some trouble-shooting tipsWithout the gas on, and in low light, turn the knob on the igniter and see if it sparks or not. It could be a rusty/dirty wire connection on the igniter or probe, or damaged wire if there's no spark. Also, make sure the probe isn't bent or broken, and that the clearancve between the probe and burner aren't excessive. The igniter unit should keep working as long as you can still hear that sharp clunk when it actuates for a spark.
I have had alittle trouble with mine lately, too. It doesn't want to light with the burner gas on high, so I back it off to med/low, and it lights fairly reliably that way.