Re: Did the Ubuntu live session corrupt my MBR?
The BOOTMGR message refers to it being unable to correctly find or use the Windows boot loader. If GRUB was still in the MBR, it would try to use that boot loader and you would see something very different.
If changing the boot order doesn't fix this (which I think it won't), you will need to do boot repair on Win7 with a repair disk or install disk.
You can also try using Boot-Repair (see link) but it has mixed results with repairing Windows boot problems: http://ubuntuforums.org/showthread.php?t=1769482
Ubuntu 15.04 Mate, Mint 17.1; MS Win 8.1, Win10 TP.
Will not respond to PM requests for support -- use the forums.