Процедура Delete

[katyakerrigan]

Помогите объяснить ошибку. Вот текст программы:
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, OleServer, WordXP,system;

type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
WordApplication1: TWordApplication;
procedure FormActivate(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}
uses ComObj;
var W:variant;
w1:WordApplication;
eee_:string;

procedure TForm1.FormActivate(Sender: TObject);
begin
W:=CreateOleObject('Word.Applicatio n');
W.Visible:=true;

end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
W.Quit;
W:=UnAssigned;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
s:string;
i:integer;
begin
s:=W.selection.text;
delete(s,1,1); //[Error] Project2.dpr(9): Constant object cannot be passed as var parameter

end;

end;

end.