Alright, apparently the issue is with the BCD (Boot Configuration Data). A few users reported that rebuilding it solved that issue.
https://answers.microsoft.com/en-us...ls-at-24/50b5fd77-5d11-431a-b4e4-9ae12cfd89a2 - "Most Helpful Reply" from Cifad
If you cannot read the commands properly, here goes (to be entered in the command prompt from the Recovery Environment):
diskpart - Opens the Disk Partitionning tool
select disk 0 - Will select your first hard drive (the one with the Windows partition on it)
list volume - Note the number of the partition that have no drive letter assigned to it, is of 260MB of size and have "FAT32" listed under the "FS" column
select volume X - X will be the number of your partition with a size of 260MB, the EFI System Partition one that you identified in the last command
assign letter=Z: - It'll assign the Z: letter to the EFI System Partition
exit - To exit the diskpart utility
Now you'll be back in the command prompt, enter the following commands:
cd /d Z:\EFI\Microsoft\Boot - Goes to the "Boot" directory in the Z: partition
attrib Z:\EFI\Microsoft\Boot\BCD -h -r -s - Removes the hidden, read-only and system attributes from the BCD folder
ren Z:\EFI\Microsoft\Boot\BCD BCD.old - Renamed the BCD folder to BCD.old
bootrec /rebuildbcd - This command will rebuild the BCD.
When it asks you
Add the installation to boot list?, press on
y followed by
Enter and if it succeed, you'll have a
The operation completed successfully message. Once you're done, close the command prompt, restart your computer and try to upgrade again.
