When you try to mount a VHD using the vhdmount tool, you may get this error message:

C:\VMs>vhdmount.exe /m DISK.vhd

The VHD file is successfully plugged in as a virtual disk device. However, VHD mount was unable to mount all volumes on the disk. Use Disk Manager to mount the volumes.

The issue is that the drivers are not signed for WHQL, so you need to follow the same steps as detailed in this blog post to make it work (as in Windows XP). Another option, however, is to set the WHQL signing option is to Ignore. This can be done through Control Panel->System->Hardware->Driver Signing:

Once you do this, you’ll be able to mount VHD files without any further errors.