UPDATE 19 August 2014 regarding KB14-045 bluescreens:
Although I don’t have a fix, there seems to be a lot of people finding this post while searching about the recent bluescreen issue caused by Microsoft Updates KB14-045. I have started a new post about this issue here:
Microsoft have now released the Full Recovery Image for WinRT (3.7GB download). You can get it here: http://www.microsoft.com/surface/en-us/support/warranty-service-and-recovery/surface-rt-startup-error-0xc000000d?lc=1033
It uses the same steps to complete the upgrade with the last part being to recreate the full recovery volume. Some news sites are saying the MS image will revert you to 8.0, it does not. It will complete the 8.1 upgrade and then the extra steps are to recreate the on-device recovery volume with the 8.0 image which only applies if you rollback sometime in the future.
First point – How annoying is it that you can only update Windows RT from the App Store, although probably not a drama if you only have one tablet. Slightly annoying if you have two. Both need to download the update, so that’s 2x the several GB needed. If you happen to be an enterprise/business that decided to buy several of them (does such a entity exist?) then it would appear you are about to have a ton of downloads happening unless you boost your proxy cache size.
And now for todays story. I updated one Surface RT with no drama. It took a long time but I just let it run overnight and it was all good the next morning. The other tablet, not so good.
Your PC needs to be repaired
The Boot Configuration Data file is missing some required information
Error code: 0xc000000d
Although it takes a while, and might be a bit tricky, it does seem to be fairly easy to recover from. (UPDATE: I have now received multiple confirmations that this works, and no data is lost!)