The Volume Shadow copy operation failed

When you try to make a Full Backup of your server using Windows Backup feature, you can get this error (See Figures below)

 

If your server runs Hyper-V with several VMs, these Virtual Machines could be the source of the problem. To check if this is the case, just open Event Viewer and go to :
Application and Services Logs -- Microsoft -- Windows -- Hyper-V-VMMS -- Admin,  then find the name of the VM or VMs which cause the problem.

After these steps, you have just to verify two things :
    - All Snapshots on this VM (or VMs) are merged.
    - There are enough free space on C:\ partition in each VM causing the problem.