For starters, Von Leon's MobID the last time I checked was 884xxxx, not 8804xxxx. 8804 ddoesn't exist because 880 is Zakum I believe, so your server is telling you that you're spawning an invalid mob that is simply null.
As for the mobs getting stuck, iirc it was because of their attacks - you needed to change something regarding their attacks in order for it to work. Also, you have to make sure the elements of their attacks along with the linked MobSkills involved actually exist within your version (otherwise you need to make a custom MobSkill Cover, or simply remove that attack).