Erro ao abrir tabela

var
Found, i: integer;
begin
ShowProgress(´Processando, por favor espere...´);
Found := -1;
for i := 0 to Screen.FormCount - 1 do
 if Screen.Forms[i] is TFrmCadSubstancias then
  Found := i;
if Found >= 0 then
 Screen.Forms[Found].Show
else
begin
 FrmCadSubstancias := TFrmCadSubstancias.Create(Application);
 with FrmCadSubstancias.IBDataSet1 do
 begin
  Open;
  First;
  FrmCadSubstancias.ComboBox1.Clear;
  FrmCadSubstancias.ComboBox1.Items.Clear;
  FrmCadSubstancias.ComboBox2.Clear;
  FrmCadSubstancias.ComboBox2.Items.Clear;
  while not EOF do
  begin
   FrmCadSubstancias.ComboBox1.Items.Add(TrimRight(FrmCadSubstancias.IBDataSet1DESCRICAO.AsString));
   FrmCadSubstancias.ComboBox2.Items.Add(TrimRight(FrmCadSubstancias.IBDataSet1DCB.AsString));
   Next;
  end;
  First;
  Insert;
 end;
 FrmCadSubstancias.Show;
 FrmCadSubstancias.SetFocus;
end;
HideProgress;
end;