Windows Server Backup returns error 24 with "Backup started a fresh backup"

Hi all,

On a Windows 2012 with the Hyper-V role installed, Windows Server Backup returns an error 24 once every two days or so with the following message:

"Backup started a fresh backup for volume '{0738191c-8456-11e3-93f2-f01fafe0878f}' ('D:') : [Reason: 'Backed up items changed to entire volume']. This may cause loss of older backup versions when backup completes."

Google returns no results for this message (ID removed of course) and I am a bit afraid of the consequences. There is a Hyper-V guest VM on the D: drive with a VHD of almost 950GB and I am guessing that the cause of the issue is here.

I am doing a Windows Server Backup to an external 2TB USB hard drive.

Anybody have a clue?

Thanks in advance,

Ambroise