http://www.quaketastic.com/files/demos/lulz2_lp3.dem
Gave it a few more runs. That particular error hasn't repeated itself, but I got other bugs while playing it. Note the fiend that glitches out in the demo! I think you may be running against some engine limits or something.
Anyway, I actually unironically like this map, and mean to record a full demo (can't promise 100% kills). It reminds me of Doom II slaughtermaps in a way. Savescumming your way through it would be a grind, but to play it through without saving you have to really think about the best route to take, the most efficient use of available powerups, etc. The demo I uploaded was the best of 6 runs, and my main problem was that I was hoarding rockets and should have used the quads on the lower level shamblers.
If you make more of these you should release them as a pack.