When adding additional backup disks to your Windows SBS 2011 server backup, you may get an error stating:

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The filename, directory name, or volume label is incorrect.

The problem occurs with the SBS console and when running the Server Backup snap-in.

You can work around this issue by manually adding the backup disks via the wbadmin command line tool.

Connect the disk you wish to add to the system. Open up a command prompt.Fetch a list of available backup targets by running:wbadmin get disks

You need the DiskID displayed of your backup disk.Add the disk to the backup pool by running:  ...