Memory access error!

I'm trying to implement a BINA with Delphi 7 using Super Bina !

I added the component in form and in botão fiz:

procedure TfrmPrincipal.btnAbreConClick(Sender: TObject);
var
  texto: String;
begin
  spBina.Conectado:=true;
  spBina.LeiaDTMF(texto,100);
  ShowMessage(texto);
end;

and no onDTMF did

procedure TfrmPrincipal.spBinaDTMF(Sender: TObject; Count: Integer);
var
  Buffer : String;
  Contador: Integer;
begin

  // Define o valor do Time Out
  Sleep(500);
  // Confere o número total de bytes dentro do pacote enviado
  Contador := spBina.InputCount;
  // Lê o pacote enviado e armazena no Buffer
  spBina.Read(Buffer, Contador);
  // Alimenta um campo Memo com os dados recebidos
  Memo1.Lines.Add(Buffer);
end;

So,    in the code of botão , on the ring of the phone line I get RING in ShowMessage . Only that!    in the code of onDTMF , upon reaching spBina.Read(Buffer, Contador); , is giving access to memory !

How do I fix this?

// Ler no modo sincrono
function TSspBina.ReadAsync(var Buffer; Count: Integer; var AsyncPtr: PAsync): Integer;
var
  Success: Boolean;
  BytesTrans: DWORD;
begin
  AsyncPtr^.Kind := okRead;
  Success := ReadFile(FHandle, Buffer, Count, BytesTrans, @AsyncPtr^.Overlapped)
    or (GetLastError = ERROR_IO_PENDING);

  if not Success then
    raise ECspBina.Create(CError_ReadFailed, GetLastError);

  Result := BytesTrans;
end;

When you do ReadFile