Suppose you have created a task sequence, advertised it and booted from task sequence media or however you want; if you receive the following error: “Task Sequence: <TS name> has failed with the error code (0x80004005). For more information, please contact your system administrator or helpdesk operator.” at Setup Windows and ConfigMgr step you might want to check the Product Key!
Most probably the key is not correct, so either write another one or remove the product key at all from Apply Windows Settings step in your task sequence and you will have to provide it during the install phase.
I left the product key blank and next time I booted the PC from the TS media, at the Setup Windows and ConfigMgr step I was asked to provide a product key. I entered my Business edition product key and everything was ok.