Error: 0x80073712 when installing KB 2919355

I do have a key for Windows 8, but this does not work even for Windows 8.

It says key is not valid of retail download!

The OEM key that comes with most computers now is apparently not valid for downloads.

It was a bad day when computer makers stopped including install media 

Makes no sense to me, only causes problems down the road. If I have a legit key I should be able to download. I suggest opening a case with MS. You won't be charged, this is a defect in their OS and not many people have opened cases. I forget how I did it but its easy.

***I have Win 8 Pro, and am not sure if Hyper-V is available to non-Pro users. If it is, great... if not, please either see if a friend has 8 Pro installed or search Google for a Virtual Manager that has a trial or is free, as a Virtual Manager will be required for those lacking 8.1 ISOs***

If anyone upgraded to Windows 8 (and are now on 8.1), they should have received 1 or 2 (possibly both) of the following two options:

1. A downloaded Windows 8 install file from Microsoft, and/or,
2. A Windows 8 DVD media that was $14.95 extra

You will need to create a virtual machine and install windows 8 onto it. Once installed, follow this tutorial to grab a Win 8.1 ISO by selecting the save to USB option. You can find Windows 8.1 MSDN ISOs on multiple software forums, such as /ware(z) dash bb dot org. If you choose this route, you must verify the md5 hash matches the md5 hash from MSDN to ensure the iso has not been tampered with. Either route will allow you to perform an install repair.

A repair install will require a generic product key for your specific version of Windows (i.e. Core, Pro, etc.)

***It appears I have stumbled upon a fix for all KB2919355 issues and will be posting this to numerous forum threads***

As many discoveries have been made, I discovered this accidentally. and quite by coincidence... 

In order for users, who've been plagued by errors and file corruption, to get a successful completion of KB2919355, all that's needed is to run the 8.1 upgrade installer, and when the 8.1 installed goes to the wait screen after entering the generic product key, start Windows Update for the install of KB2919355

Steps

1. Run the Windows 8.1 installer from within Windows, as if you're going to do an install repair "upgrade".
2. Enter the generic product key, and upon clicking next, the installer will say wait...
3. Give the installer about 5 minutes, then start Windows Update (it should show the KB2919355 update), and click install.
4. Windows Update will begin downloading the update... if you have a Windows Update cache problem that causes the speed and percentage to remain at zero, don't worry about it and get the update installed first, then you can clear the cache and remove the directories afterwards.
5. The install may fail, don't worry... simply hit install again, making sure the 8.1 installer screen is still on the "wait" screen, as whatever the installer is doing during the "wait" screen is what makes the KB2919355 install possible.
6. KB2919355 should install and Windows Update should request you to restart... simply do so without cancelling the 8.1 installer.  Windows will finalize the update during the shutdown and restart processes.
7. Upon rebooting into Windows, you will have a multitude of additional updates that will need to be installed (around 10, give or take a few), and you can verify the install of KB2919355 by going to "view installed updates"

A few users will need to comment back once they'e performed this in order to see if this automatically fixes the multitude of issues users are facing, and if it doesn't complete successfully, then I can back track what step I took over the past several days in order to figure out what caused this to work for me, but not others if problems occur.

Are you trying to download Win 8 OR Win 8.1?  Even though 8.1 has an eight in it, it's essentially a new OS for all intents and purposes.  Generic keys DO work, but you have to have the correct generic key for your version of Windows.

For example. a Windows 8 activation key WILL NOT work, period.  This key is meant for activation and activation only... not for the installer.  The installer requires a generic key that is for your specific Windows version (i.e. Core, Pro, etc.).  You can not install Windows 8.1 with a Windows 8 generic key, as Windows 8.1 has it's own generic keys for different Windows versions.  All generic keys are readily available via Google.

As far as why Microsoft chose the generic vs. activation keys, I can only surmise it's due to their licensing structure change, going from 3 to 1 PCs and recognizing that a user needing to input their activation key every time they need to install Windows 8/8.1, then again to activate Windows 8/8.1, could cause it to be sent out as 2 separate activations.