problem z obsluga dll

library D66;

{$R *.res}

function D66Koduj(S: String): String;
var
 I:integer;
 Tmp: String[255];
begin
 if Length(S)=0 then exit;
 for I:=1 to Length(S) do
 begin
  Tmp[i]:=char(ord(S[i])+66);
 end;
 result:=Tmp;
end;

function D66Dekoduj(S: String): String;
var
 I:integer;
 Tmp: String[255];
begin
 if Length(S)=0 then exit;
 for I:=1 to Length(S) do
 begin
  Tmp[i]:=char(ord(S[i])-66);
 end;
 result:=Tmp;
end;

exports D66Koduj, D66Dekoduj;

end.

Unit Unit1
...
...
const
 libname = 'd66.dll';

function D66Koduj(S:String):String;external libname;
function D66Dekoduj(S:String):String;external libname;

procedure TForm1.btnKodujClick(Sender: TObject);
begin
 edtdekod.Text:=d66koduj(edtkod.Text);
 edtKod.text:='';
 btnKoduj.Enabled:=not btnkoduj.Enabled;
 btnDekoduj.Enabled:=not btndekoduj.Enabled;
end;

procedure TForm1.btnDekodujClick(Sender: TObject);
begin
 edtkod.Text:=d66dekoduj(edtdekod.Text);
 edtDekod.Text:='';
 btnKoduj.Enabled:=not btnkoduj.Enabled;
 btnDekoduj.Enabled:=not btndekoduj.Enabled;
end;