Oh and just tested the "descr_projectile" quickfix file you put up - it actually still causes a crash in game when the Goblin Doom Diver and the Earthshaker Cannon fire. But the Death Rocket seems to be working fine which seems weird .
The only difference I can see between the "descr_projectile" I edited myself and the quickfix on the second post is the length of the path reference for the .cas files. I seem to have my path references for those 3 .cas files as "mods/Rage_of_dark_Gods/data/models_missile/...", whereas your file has a shortened version of "data/models_missile/...". Maybe it needs it to be more specific for some reason? I have no idea, but the Goblin Doom Diver and Earthshaker definitely don't seem to work for me if I use the shorter path reference. They work fine with the longer path though :S.
I attached my "descr_projectile" file where they all work if it's any help .