This article describes how to resolve the error "A Volume (drive) that was previously backed up is no longer there and being backed up", as shown in the following image:
The most common cause of this error is a selected drive missing when a backup runs. To resolve this issue, bring the missing drive back online. Once the drive is online, the error clears upon the next backup.
For example, you add a data source and select to back up drives C and J on the Backup > Sources page:
After a few successful backups, the J drive goes offline and the next backup report displays the warning message:
Go to the Backup > Sources page and view the data source; the drive J is missing:
Bring the missing drive back online to resolve the error once the next backup is run.