I am not sure if it is the same thing or not, but I can't multicast either.
* Server setup for multicasting (needing four clients to start)
* Using WinPE 2.1 with all drivers selected (no UNDI issue)
* I kicked off 48 images at once, and my script has a "Run Script" pause in it so that I can be assured all computers are ready before I kick the process off.
The computers all start displaying notices like;
* "Becoming counting master"
* "Becoming counting client"
* Becoming negoiating master"
* etc
After a few minutes (probably the default five minutes actually), all of them start to unicast. Not cool.