Most likely the thermocouple is bad, they go out, it happens with pilot light apps. See, the pilot light heats an element up, that 'hot' element tells it, YES there is a pilot light, so it's OK to turn the main gas on. You turn the gas on, if the temp detector says it's ok to do so, the valve opens up, the pilot light ignites the main burner gas and viola you have heat for your beans. When that little sensing element goes bad that gets hot, then it won't send the signal to the main assembly saying it's ok to turn on the gas, therefore when you say gas on, it says, umm NOPE.
Replace that as you said you are and it should hopefully fix the problem.
Again, this is just an armchair troubleshooting, I can't actually TELL you what's wrong without actually looking at it, but from past experiences with burners and stuff, that sounds like the issue. A new assembly is what 30 dollars or so?
Aaron