Veritas Backup Error "0xe00084af - The directory or file was not found or cannot be accessed"

I have a customer who still runs Veritas Backup Exec version 9.1 and I had recently upgraded WSUS to version 3, I noticed that the overnight backup was now failing each time with the error in the post title.

If I tried to backup any file from the C: drive this error would occur event though the files were accessible in Veritas, a backup of the Information Store or Shadow Copy was successful.

The cause of the error is the SQL Server VSS Writer Service that is installed as part of WSUS 3 application and if this service is running it will cause the Veritas Backup to fail.

All you need to do is use the Pre and Post Backup files to stop and start the service and you can continue to backup as normal and avoid this rather ambiguous error.