Note: This was posted in the home section here by mistake and again posted in the business section here https://forum.eset.com/topic/3861-server-2012-r2-backup-and-eset-nod32-failure-compacting-virtual-hard-disk/ , but the replies occurred here.
Note: My original issue with Windows Backup had nothing to do with Eset after all.
I am using ESET File Security for Microsoft Windows Server - a product designed for servers:
hxxp://www.eset.com/us/business/products/file-windows/
In this product, if you select to exclude *.vhd it automatically adds the drive letter when you click OK:
C:\*.vhd
D:\*.vhd
This strongly implies that if a new drive, say E, is added it will not exclude *.vhd on that new drive.
I have not tested this by adding a new drive and going back to exclusions to check if it is added automatically.
This should be corrected by Eset, if not just the exclusion section which should technically be listed just as entered by the user:
*.vhd --- Exclude any file with an extension of .vhd on any drive, anywhere, any time.
NOT:
C:\*.vhd
D:\*.vhd