umm, one thing for the win7 uefi booting method the letter is not of consequence, it uses the partition "ID" now.
the BCD junk is (usually) a small partition with the boot stuff in it, then that passes over to the partition with the os in it.
If you got an error like that, you would want to know previously what and where these partitions are, just so you know what your dealing with , when stuff changes.
sorry i dont really know enough because i despise the method.
when you get the I/O error it could mean friggen anything (like all errors) but at that time a persom might want to check the viability of the drive itself WithOut writing to it, or doing chkdisk stuff. There are certian types of problems that checkdisking can make worse :-(
A linux person would want to hop into some portable boot of some sort and do a check of the drive from "outside" and see what was up. A windows person would want to have some bootable USB or disk tool stuff with a gui :-) and do a quick check of the disk.
From some disk tool a person would want to see how the array of partitions looked. Like the rapaar one, and the recover one, and the "system" one ( the one with BCD stuff) and the OS one. (again what purpose is served for having complicated the structure so) so you need to see is the disk working, is there an intact partition table/structure.
Back at the ID of the partition. this stupid (imo) first partition has on it a few programs for doing the passing from the uefi to the boot , that first small partition is what has the "bcd" from that crap, it finds the partition with the actual OS on it, based on the ID. and an ID change on the OS partition would leave the BCD itself lost.
So go back a bit, if it claims it cannot find the BCD, then it could be things like the wrong Disk. or simple stuff like the UEFI/BIOS isnt set to boot to it . I would have started back at the UEFI, for the purpose of seeing if the disk is working (init on the motherboard will have scanned the disk and at least know it is there). You believe it is seeing that disk, that has not been proved.