Multicast works, when I manually boot the pcs to pxe, and the TS kicks off. If I run the same TS to do an in place upgrade (an OS is already on the pc), the TS kicks of, boots to winpe and then gets stuck on opening the multicast session and eventually times out. Any advice would be greatly appreciated.

check your multicast settings for different boot images (sounds like you are using more than one depending on the advertisement of the task sequence in question, Step by Step ConfigMgr 2007 Guides | Step by Step ConfigMgr 2012 Guides | I'm on Twitter > ncbrady

http://technet.microsoft.com/en-us/library/bb693631.aspx This Link 'll Help You DushYant

You are trying to run tasks to do In-place Upgrade, which means run upgrade withing the existed Windows system. However multicast will only work in WinPE. That may be the problem. You may let us know what the TS will do. For more information regarding multicast, refer to: http://blogs.msdn.com/b/steverac/archive/2008/10/19/setting-up-multicasting-in-sccm.aspx Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Thank you for your reply, ultimately it was a network issue and the network guys had to allow some ports through on the router, all is well now.

I am having the same problem here, PXE booting all computer's here will Multicast, if I try and setup mandatory task sequence to image a lab of computers they all establish a unicast session. Any suggestions ? My computer's are booting to PE also.