Runtime Error /mte.lua Line: 11616 when badguy is killed

Hi, thank you in advance for any help you might have on this: when I kill some of my bad guys and they disappear, This air seems to randomly show for only some bad guys. I don’t have lights applied to these bad guys but there is a light around the player shines into the darkness. I am removing the movement timer that each bad guy has when they die - that is handled okay. 

Error screenshot: http://screencast.com/t/NeeSXf3W0

/mte.lua Line: 11616 talks about lighting it seems:

local levelDiff = math.abs(M.getLevel(i) - map.lights[key].level)

Console says this at the same time: 

2014-08-17 17:03:12.987 Corona Simulator[70200:507] Runtime error

…lumes/Work/home/!!IPAD GAMES/raiders/Raiders/mte.lua:11616: attempt to index field ‘?’ (a nil value)

stack traceback:

…lumes/Work/home/!!IPAD GAMES/raiders/Raiders/mte.lua:11616: in function ‘update’

…umes/Work/home/!!IPAD GAMES/raiders/Raiders/main.lua:1176: in function <…umes/Work/home/!!IPAD GAMES/raiders/Raiders/main.lua:1140>

?: in function <?:218>

 I do notice that from time to time so my bad guys do seem to glow green (the same green glow that I’ve given to my fireflies) but I don’t know why some of the bad guys would glow green and those guys always have this error happen. Again to me, it appears to be random which bad guys have this problem.