I came across this issue, when I prepared a Windows 8 vhd and attached the vhd to the Windows 7 Enterprise System. After attaching the vhd, I run the bcdboot command to boot the Windows 8 from the vhd.

bcdboot.exe G:\Windows

This command given the error ” failure when attempting to copy boot files”.

Solution:

Run the command prompt under administrator previlage.

Start-> right click Command prompt-> Select “Run as Administrator”

Now run the bcdboot to add the new OS to the boot list.