I run a few VM's on my workstation to perform different tasks one is a Windows 8 dev box, I finally got around to upgrading it. So checked all updates were done and then went to the store to get an error message I think is somewhat unusual.
Sorry, you can't install the update because it isn't supported by your computer's CPU.
So quick search online didn't yeild any obvious results and a simple setting came to mind that may fix it. When choosing your VM you select your version of Windows so after switching it to 8.1 it worked magically (well not magically but you get my point).
Then nipping back into the Windows Store and all works fine. Message of the day -- thinking a little helps!