When attempting to backup virtual machines hosted on a Hyper-V that were previously converted from a physical machine using any conversion tool the backup may fail with one of the errors below.
Job Log errors:
V-79-57344-38721 - Failed to mount one or more virtual disk images
0x1d - The system cannot write to the specified device.
Debug Log Errors:
bevs::IVhdFileUtil::create_VHDX_from_handle: invalid virtual disk size
A hotfix is now available for this issue in the current version(s) of the product(s) mentioned in this article. Refer to the Hotfix link under Related Documents at the end of this article to obtain the hotfix needed to resolve the issue.
Backup Exec 2014 Rev 1786 Service Pack 1 (TECH216178).
Backup the effected virtual machines as if they were a physical machine.
Resize the VHD to the nearest megabyte.