SQL Backup Incremental Errro

My BE Appliance keeps reports failed for the incremental job failure ... while the same setting FULL backup is successfully executed everytime. 

 

03 Sep 2013  09:45:22 AM

Computer: [SERVER NAME( SERVER_IP)]

Monitor: [Event Log Monitor]

Description:

* Event Time: 03 Sep 2013 09:35:18 AM

* Source: Backup Exec

* Event Log: Application

* Type: Error

* Event ID: 34113

* Event User: N/A

* Backup Exec Alert: Job Failed

(Server: "BEAPPLIANCE") (Job: "app-sql2 Backup 00004-Incremental") app-sql2 Backup 00004-Incremental -- The job failed with the following error: The Backup Exec SQL Agent was not used to create the last full, differential, or log backup of this database. You must use the SQL Agent to run a full backup before you can run a differential backup or transaction log backup.

 

any idea where do i missed ?