Error: 0x80073712 when installing KB 2919355

That's a great question, seeming as the only way to gain access to an 8.1 iso was when a person upgraded from 8 to 8.1 and chose the option to save the files to usb or iso.  Since the Microsoft application that was used to upgrade from 8 to 8.1 no longer accepts valid or generic product keys, it now becomes impossible to even create a virtual machine with Hyper-V, install 8, download the Microsoft 8.1 update application and save the installation files.

While that was the easiest way to gain access to them, the other more difficult route is to run 8 from a virtual machine and use the windows store to update.  The problem is, I can't recall where Microsoft downloads the install files too... if memory serves right, it was to the user's temp files in app data - local, however I can't find the bookmark of the page that gave instructions on where to find the downloaded files at.

Seeming as Microsoft created this problem they should be the ones to make the media available to users, and while you expect malware to corrupt system files, you never dream of an OS manufacturer corrupting their own OS's system files via their own update and update software... this level of corruption is literally unheard of.  And since Microsoft refuses to give access on their site, other than subscription based MSDN or TechNet, to an 8.1 ISO, the only way to get the ISO if the user didn't take steps to when they upgraded from 8 is to download the ISO from a software forum and check the sha1 hashes to make sure the ISO hasn't been tampered with.

EDIT:

While I don't normally suggest software forums for a number of reasons, I don't agree with telling anyone they should have to wipe their system, reinstall 8, and go through the tedious hassle of reinstalling every bit of software simply because Microsoft screwed the pooch, took the cake, and ate it too.  I have little patience with Microsoft at the moment due to their idiocy of refusing to give users actual troubleshooting steps that would do something, instead of the cookie cutter response the same microsoft moderator (the one whom started this thread on page 1) gave on 4 or 5 of the 6 forum threads dedicated to the top 6 errors received from the mucked up KB2919355 install.  As far as Microsoft goes, downloading an 8.1 ISO from a software forum shouldn't be a T & C issue since Windows 8.1 is free and does not have it's own line of Activation Keys.  Since users downloading it from a Software site would be doing it to fix a windows installation that's already been activated, I would hope moderators would give a little leeway on this subject... although I also understand if none can be given.

I found it SOOOO ironic when I asked the MS Tier 3 tech where this "corruption" came from: "Malware...viruses..."

REALLY? In that case, MS is distributing malware, cause this system is clean as a whistle. Avast 2014 + Malwarebytes Pro + routine scans + no unsafe practices like clicking links in emails, going to questionable sites, etc. Then the implication on this message forum that "it's something the user did while installing 8". Excuse me?? 

Granted, if you're having issues, MS Tech support WILL help you. When I opened a case via chat, the moment I described the problem they escalated it direct to Tier 3, who were nice, helpful, patient, and ..... well, not sure how competent. But it works now.

I apologize, I thought you had been able to get that repaired.  You can get an 8.1 iso, but it would have to be from a software forum.  As long as you're diligent and verify sha1 hashes with Microsoft's sha1 hashes, you'll get a win 8.1 iso that hasn't been tampered with.  I have to get a bit creative here, otherwise this will be edited automatically.  There's a software forum I use on a regular basis and a member whom I trust that has never posted software with malware... her name is *******and the forum is ****** Hopefully that was creative enough :)  You'll need to register for the apps section to be listed; registration is free.         

wow they censored you fast...I'd like to know this...

BTW can I put my Win 8.1 x64 ISO up somewhere for people to use? I mean after all they would be using their own keys, they own the software license, they just need the data....That's not illegal or against forum rules is it?

I would love a pre-made ISO of a Win8.1 PE environment that I could Rufus onto a thumb drive...I've tried working with WAIK before, man what a hassle. I'll check out your links.

For now I just have a multi-boot USB stick made with Sardu, that lets me use gparted or kubuntu or Hiren's or DOS ntpasswd - whenever I need to work on my partitions or BIOS etc I use that. But the greater functionality of a true PE environment would be nice.