How to Insert a NEW Sales Order Using Code

Hi, I am trying to import TAB separated file consist of 4 columns. Each row is a New Sales Order. at the
Integer - Import::OnBeforeInsertRecord() i Wrote the following Code,
SalesHeader.SetHideValidationDialog(TRUE);
SalesHeader.INIT;
SalesHeader."Document Type" := SalesHeader."Document Type"::Order;
SalesHeader.INSERT(TRUE);
but for second record i got Error, that Sales Header already Exists.

Not sure what is wrong in this.