Incremental failed

I tried to backup to disk, the full backup is ok but when it tried to do incremental, it failed. Could someone tell me what does it mean and how to resolve.

Here the error is:

Backup Data Base-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.

Regards,

Tho.