I am testing the results of tut 21. I go to the battle and attack. The particle starts then I get the exception. I can unpause the editor and the battle continues. I switched to use particles from Cartoon FX Pack by Jean Moreno (JMO) with the same result. My first thought is that it looks like the deprecated ParticleEmitter is finally removed. I am about to switch from the Ork dll to source code to debug this.