Backup Exec 2012 won't delete previous backups on USB drive

Situation
Windows 2011 SBS Server with Symantec Backup Exec 2012 running.
Backup written on USB disks. 5 disks wich were changed every day. One disk has enough space for 1 full backup.
Seperate job for every day
Retention periode 4 days

Problem
We have to delete every day the previous backup set manualy backup backup exec won;t do this for us

Solution all ready treid
http://www.symantec.com/business/support/index?page=content&id=TECH187957&profileURL=https%3A%2F%2Fsymaccount-profile.symantec.com%2FSSO%2Findex.jsp%3FssoID%3D1374758045215GrH8s2knSsBJ42095fug1XRjvY8n7FtM6wx5R

Without any results.