We've discovered a bug in Red that stop you from building pack files for user made levels. It only happens if you have a particle emitter in your level that uses the default particle emitter texture (Rck_DefaultP.tga). It's really ease to get around. Simply put this texture (make "this texture" a link to the attached targa) into your ".."RedFaction/user_maps/textures" directory and you will be all set.
/ should be facing the other way but the site won't allow it.