Beremote Debug shows:
BEREMOTE: [4444] [fsys\shared] - VDDK-Log: VixDiskLib: VixDiskLib_ReadMetadata: Missing metadata value. Error 16052 (The specified key is not found in the disk database) at 8705.
BEREMOTE: [4444] [fsys\shared] - VDDK-Log: VixDiskLib: VixDiskLib_ReadMetadata: Retrieve metadata value.
BEREMOTE: [4444] [fsys\shared] - VDDK-Log: VixDiskLib: VixDiskLib_ReadMetadata: Missing metadata value. Error 16052 (The specified key is not found in the disk database) at 8705.
The problem seems to be with the Virtual Machine registration on the VCenter or ESX.
The below steps can be tried if the beremote debug is found matching to this technote.
1. Remove the particular virtual machine from inventory within VCenter and then re-add it.
OR
2. Move the particular virtual machine to a different ESX host or export the problematic virtual machine from one ESX Host and import it to another and then test the backup.