These are the files that match your error, couldn't be sure on which "missile 3" you needed so I uploaded both. Navigate to "drive letter:\***\Steam\steamapps\common\Sacred 2 Gold\scripts\particle" and place the missing files there, as according to that error they should be missing. If Windows asks you to overwrite try doing so after creating backups of the original and see if the exception still occurs.
x_gen_missile3.particle
fx_gen_missile3.particle
x_stone_streak.particle
That error sounds like something went wrong during the installation of one the additional components, or it could be that one of the mods isn't compatible with the rest (I'm looking at the Reduced Fog mod to be honest since the rest is by now fully compatible). By the way, did you download the more recent version of Enhanced Edition or are you using the old one?