[marcoszorrilla]

Aquí tienes un ejemplo completo que funciona correctamente.

Código Delphi [-]
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, DBTables;

  Procedure midberror(DataSet: TDataSet; E: EDatabaseError);

type
  TForm1 = class(TForm)
    Table1: TTable;
    DataSource1: TDataSource;
    procedure Table1PostError(DataSet: TDataSet; E: EDatabaseError;
      var Action: TDataAction);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
Const
  eKeyViol = 9729;
  eRequiredFieldMissing = 9732;
  eForeignKey = 9733;
  eDetailsExist = 9734;
  eSqlGralerror = 13059;
  eInvalidTime = 10058;
  eInvalidDate = 75;
  EinvalidDateTime=10060;
  eRegisterLocked= 10241;
implementation

{$R *.DFM}

Procedure midberror(DataSet: TDataSet; E: EDatabaseError);
begin
if (E is EDBEngineError) then
    if (E as EDBEngineError).Errors[0].Errorcode = eKeyViol then
    begin
      Application.MessageBox('Imposible dar alta ese registro ya existe','Atención',mb_Ok +
mb_IconQuestion);
      Abort;
      end;

if (E as EDBEngineError).Errors[0].Errorcode = eRequiredFieldMissing then
    begin
      Application.MessageBox('Imposible dar alta hay un campo vacio.','Atención',mb_Ok +
mb_IconQuestion);
      Abort;
      end;

      //campo en blanco

      if (E as EDBEngineError).Errors[0].Errorcode =   eSqlGralerror then
    begin
      Application.MessageBox('Imposible dar alta hay un campo requerido vacío.','Atención',mb_Ok +
mb_IconQuestion);
      Abort;
      end;

end;

procedure TForm1.Table1PostError(DataSet: TDataSet; E: EDatabaseError;
  var Action: TDataAction);
begin
MiDbError(Table1, e);
end;

end.

Un Saludo.