I have a slightly different problem with the same error message.
My XP sessions began failing (probably after a couple of premature shutdowns) and gave me blackscreen startups so I deleted the current .vhd file and replaced it with a ten-day old backup (always keep a backup
However, this is now giving me the error message on startups:
VD: error VERR_VD_VHD_INVALID_HEADER ....(VERR_VD_VHD_INVALID_HEADER)
I can't use the Discard option because it's not highlighted.
I'll explore two options, repeating the copy of the backup, or creating a new XP by importing the backup, but any other options or suggestions will be helpful.