There are a number of possible causes. First, check the VHD file security. You need to ensure that you're logged on as a local Administrator, and that the NTFS permissions on the VHD are set so that the System account and the local Administrators account have Full Control. The Users group should also have Read and Execute permissions.
If the virtual hard disks are on a file server, you need to ensure that they're connected via a Universal Naming Convention (UNC) path (you can't use a mapped drive or mount point), and that the Hyper-V computer account (domain\computername$) has Full Control VHD-file permissions and it's on the share containing the VHD.
The solution that worked for me was to remove the device from the VM, then add it again using the following procedure:
- Select Settings for the VM experiencing the problem.
- In the Hardware menu, select the problematic VHD hard drive and click the Remove button, as Figure 2 shows.
- Select the IDE controller, then the hard drive virtual-disk file, and click Add, as Figure 3 shows.