Well, in the last LOD you can't have more than 300 polys (I think I'm not sure by head) but that isn't the problem since you already have a shadow on.
Another possible thing, is the name of the model not defined well in the cpp file, check if in the config models section the name of the .p3d file is exactely the same as you called it in the filed.
One of the 3 options I gave you, must solve the problem.
1 The Muzzle Flash names as a section called Zasleh in all tle LODS.
2 Erase the Muzzle Flash from the last LOD.
3 The name of the model in the cpp file