Why use SQL Server 2008 maintenance plans designed to automatically back up the database, after running only to find that no backup?

I use SQL Server 2008 maintenance plans designed to automatically backup specified database:
    12:00 every day automatically backup specified database "commodity inventory management," the backup file on the "E: \ commodity inventory management data backup" folder. Designed to backup files kept for 3 days, before automatically delete backup files are backed up more than three days after the database every day.
    In the design process, "created for each database backup file" column enter is: "E: \ data backup product inventory management." (Note:. E disk has previously built the folder "commodity inventory management data backup") in the "backup file extension" column enter is "bak".
    It has opened a "SQL Server Agent" in the Object Explorer. In SQL2008 "Configuration Manager": the SQL Server Agent (MSSQLSERVER) is set to "start automatically."
    However, after running the software, E disk file in the folder "E: \ data backup product inventory management" has not been found in the backup file appears.
    King ask a computer expert, why? How to set correct? Greatful!