Hmm - the file looks ok to me.
Anyway - move the vmsd -file to a different directory and add the file I attached to the same directory as the flat.vmdk
Then try to mount that one.
If that still does not work - which architecture do you use ? 64bit or 32bit ?
try to mount it with winimage - or in case you use a 32bit host try vdk.exe - see
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