Microsoft released a KB article for when Backing up virtual machines fails when using the CSV writer after installation of update 2919355 in Windows.
Assume that you install update 2919355 on a Windows 8.1-based or Windows Server 2012 R2-based computer. When you try to back up some Hyper-V virtual machines that reside on cluster shared volumes, you receive an error message that indicates the backup request has failed.
Here is a sample of the error messages that you may encounter when this issue occurs:
Csv writer is in failed state with unexpected error
Note The error message that an end-user will see is surfaced by the backup vendor products, and therefore it will vary by vendor.
A hotfix is available to resolve this issue.