Option to delete an old backup destination is greyed out (SSR 2011)

This post concerns Symantec System Recovery 2011, using the stock, built-in GUI (i.e., not the Management Console).  I'm trying to delete a drive as a backup destination, as the drive is no longer available.  When I go to Tools|Manage Backup Desintation|Tasks, the Delete option is grayed out for the drive I'm trying to delete as a backup destination.

Thanks.