To resolve this problem please use “Regen Backup Store Groom Tool” which can be used to delete the existing old Backup stores. You can download the above tool from the following URL
http://www.techsupportlive.com/index.php?_m=downloads&_a=viewdownload&downloaditemid=56
To know more about Regen Backup store groom tool please refer to the document with the following URL:
http://www.techsupportlive.com/index.php?_m=downloads&_a=viewdownload&downloaditemid=58