There's a workaround for it.......but probably not M$ approved...:bigsmile:
It seems that you can upgrade from a certain iso with a testing key from Microsoft,but can't activate it with that key.(which is good,of course!:iagree:)
However,after the installation,you can feed your own, legal obtained key to the activation window and get a fully activated version.
If you also have a legal key for Windows Media Center,you can use it to get a 8.1 Pro Media Center Edition.....