I received rejection 'BL Already on File'. What does it mean?

I received rejection 'BL Already on File'. What does it mean?

Reason:
The manifest with the shipment was sent twice.
Resolution:
1. Ask for support’s assistance to set the shipment status to Accepted (backend) so that it may be resubmitted as Modify.
2. If the rejection still persists, the PAPS number may have already been used in the past and a new PAPS number must be provided in order to proceed.

Resolution if PAPS has been previously used:
1.       Provide another shipment control number
2.       Change the existing SCN or PAPS number.
3.       Save the shipment
4.       Save the manifest
5.       Resubmit as ADD
NOTE: Make sure to inform the Broker regarding new SCN so they can process again using the new SCN.