gnat serial communication

[Rolf <rolf.ebert_nospam_@gmx.net>]

I am having a hard time getting back to programming with GNAT

I installed GNAT GPL 2011 on a windows XP SP3 computer together with
GTK-Ada.

The current task is to simply display the incoming data from a serial
line to the console. The following program always fails displaying the
message:

raised GNAT.SERIAL_COMMUNICATIONS.SERIAL_ERROR : set: cannot get comm
state ( 6)

with GNAT.Serial_Communications;     use GNAT.Serial_Communications;
with Ada.Text_IO;                    use Ada.Text_IO;
with Ada.Streams;                    use Ada.Streams;

procedure Read_Ser is
   P_Voltage : Serial_Port;
   Voltage_Buffer : Stream_Element_Array(1..11);
   Voltage_Last   : Stream_Element_Offset;
begin
   Open (P_Voltage, Name (11));
   Set (P_Voltage, Rate => B19200);

end Read_Ser;


The corresponding code in GNAT.Serial_Communications is

     Success := GetCommState (HANDLE (Port.H.all),
Com_Settings'Access);

      if Success = Win32.FALSE then
         Success := CloseHandle (HANDLE (Port.H.all));
         Port.H.all := 0;
         Raise_Error ("set: cannot get comm state");
      end if;

Other terminal programs (HTerm, Bry_Terminal, etc.) connect to the
port without problem can display the incoming data. Does anybody know
what might be problem here?

Rolf