What does "Cannot create a record in Header (AVA_Header)" mean?

Overview

Whenever you try to post an Invoice following error comes up :

"Cannot create a record in Header (AVA_Header). The record already exists"

Environment

Microsoft Dynamics AX 2012

Resolution

• Verify the number sequence of Header Id. The number sequence name is AVA_Head.
• Make sure that "Continuous" is not selected.