These errors are always difficult to nail down :-(

I'd start here.

If you click on 7B in the left hand column, the pre-amble says

"Windows lost access to the system partition or boot volume during the startup process. 
Typical causes: Installing incorrect device drivers when installing or upgrading 
storage adapter hardware, or a virus" . . . 

. . .and is followed by some references which may provide clues to what is happening 
on your system.

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