GSS 3.0 Multicast Options Greyed-out, Why?

Just got the new GSS 3.0 setup and ready to go. Little bit of a learning curve, but not to bad so far. HOWEVER, when I create a Distrubute Disk Image task and I want to deploy it to a group of worsktations and do a mulitcast, the option is greyed out, why? What option am I missing that needs to be enabled or re-configured? I am not seeing an easy way to set the automation pre-boot enviroment to a Windows PE that I have setup and configured already, is that something I am missing? Please help!

Thanks

Brad