delphi 中UDP 通讯问题。请高手指教！急！！！

程序如下，但是总是报错。错误内容在插图中，请高手务必帮小弟看看问题出在哪里。
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs,Sockets, StdCtrls,ExtCtrls,IdUDPServer, IdSocketHandle,IdBaseComponent,
   IdComponent, IdUDPBase, IdUDPClient;


type
  TForm1 = class(TForm)
    GroupBox1: TGroupBox;
    GroupBox2: TGroupBox;
    ComboBox1: TComboBox;
    Memo1: TMemo;
    Memo2: TMemo;
    Button1: TButton;
    IdUDPClient1: TIdUDPClient;
    IdUDPServer1: TIdUDPServer;
    procedure FormShow(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure IdUDPServer1UDPRead(AThread: TIdUDPListenerThread; AData: TBytes;
      ABinding: TIdSocketHandle);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
Tcommblock = record//
      sendername,
msg :string[20];//消息，每次发送的消息的字节数
      end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
comm: TCommBlock;
begin

  comm.sendername:=combobox1.Text;
  comm.msg:=memo2.Text;
  memo1.Lines.Add(comm.sendername+':'+comm.msg);
  idudpclient1.SendBuffer(comm.msg,length(comm.msg));

end;

procedure TForm1.FormShow(Sender: TObject);
begin
   IdUDPClient1.Host:='';
   IdUDPClient1.Port:=8080;
   IdUDPClient1.ReceiveTimeout:=5000;
   IdUDPClient1.Active:=true;

end;

procedure TForm1.IdUDPServer1UDPRead(AThread: TIdUDPListenerThread;
  AData: TBytes; ABinding: TIdSocketHandle);
var
comm:TCommBlock;
begin
   adata.Read(comm,adata.size);
   memo1.lines.Add(comm.sendername+':'+comm.msg);
end;

end.