You may have run into the issue where you boot into WinPE and get the very common “No Task Sequences are available (TaskSEquences.XML does not exist, is empy or inaccessible.” I ran into this for the very first time after upgrading from MDT 2008 Update 1 to MDT 2010.
You then go and validate that the TaskSequences.XML in the control folder of your deploymentshare has data in it and is not corrupt. I noticed that when I canceled out of the deployment wizard, deleted the MININT directory with the following command: rd C:\MININT /q/s – and restart the litetouch.wsf, I do not get the same error. I can then select my Task Sequences as expected.
A tip to debug this issue is to add the /debugcapture when you start the litetouch.wsf script.You can edit the Windows PE Unattend.XML and add the /debugcapture after the litetouch.wsf in the RunSynchronous section. The value on the right side states to run wscript.exe x:\deploy\scripts\litetouch.wsf, just add /debugcapture to the end of it. After making this change you will need to regenerate your boot image with MDT 2010. Then start the process by booting and view the log file when you are done. This might give you some additional information in the BDD.log
Often the issue involves the DeployRoot value isn’t quite correct. Tim Minter does an excellent job discussing this on his blog: http://deployment.xtremeconsulting.com/2009/11/13/the-case-of-the-disappearing-task-sequences/