In my experience using existing Windows VMs as a "helper VM" for expanding other Windows VMs is an absolute no go.
It is neither necessary nor useful.
Always either use the guest OS itself for expanding the drive - Win7 and later support that natively - for XP and 2003 use dells extpart.
If that is no option either use Windows PE-CD - as they do not mess with disk-signatures or driveletters or use Linux LiveCDs