use this server.cs instead. I've fixed all errors for you.
on a side note, make sure you place all of your color files that are on the gun (if you have a material named "brown" place brown.png into your file.) it just needs to be a 16x16 square in paint filled with brown. also, rename your model to "heavyGun.dts". Make sure when exporting that all of your groups have a LOD of 0.