Thank you for posting it!
Was there a time where FFXIV was running well consistently? Or has it always been kind of crashing to the desktop? Was there a particular FFXIV patch that you noticed it start to go bad? Have you installed new memory / different memory since the time it was working?
Any power outages recently (if yes, are you using an UPS or surge protector)?
If you grab another game from Steam, be that a free game or no, to see if it'll let you install it or if it'll be corrupt. (don't uninstall ones you have, grab maybe one of the free, large ones like DC Universe or Alpha Protocol something, the former may require patching to simulate some situations).
On the FFXIV update when does the error message occur? Right at the beginning before updates begin, when the update bar has progressed some, after the update window ends and is attempting to install the files?
Do you have a standard mouse you can try instead of the Razer mouse or that Death mouse that seems to be listed in your specs. I know it's silly, but some people's crashes have been side effects such as disabling the vibration of their gamepad, unplugging a USB gamepad, and a handful of other things.
And the last and possibly more difficult to find, a memory test on your RAMs.
There's this program for the Memtest86+ link:
http://www.memtest.org/#downiso
Or perhaps not as robust, the windows built-in Memory Diagonstics Tool (Start Menu, I type Memory and it shows up, I don't think I had to download it). It should pop up and ask if you want to restart your computer. Go through the steps to see if anything comes back with errors.
I think others far far far more qualified than I may see this sometime throughout the week.
I has a feeling these issues are all linked and if we resolve the one, may end up fixing the corrupt file installation, the updater error, and the occasional crashing to desktop.