VAR
  Registry : TRegistry;
  WriteReportToRegistry : Boolean;

begin
  WriteReportToRegistry := True;
  Registry := TRegistry.Create;
  Registry.RootKey := HKEY_LOCAL_MACHINE;

  if Registry.KeyExists('\Software\SysIT\Nails4You') = False then
     Try
        Registry.CreateKey('\Software\SysIT\Nails4You');
     Except
        Registry.Free;
          WriteReportToRegistry := False;
          Registry.WriteString ('Mandant', DBEdit_MandantNr.Text);
        Exit;
     END;

  Try
    if Registry.OpenKey('\Software\SysIT\Nails4You', True) = True then
       Registry.WriteString ('Mandant', DBEdit_MandantNr.Text)
       ELSE
          Begin
              MessageDLG('Es konnte nicht in die Registry geschrieben werden', mtError, [mbOK], 0);
              Registry.WriteString (DBEdit_MandantNr.Text, DSN);
          End;

  Finally
      Registry.CloseKey;
      Registry.free;
  End;

procedure Tfrm_Main.Button1Click(Sender: TObject);

var Registry: TRegistry;
var Test : String;
var mandant : String;
begin
  Registry := TRegistry.Create;
  try
    Registry.RootKey := HKEY_CURRENT_USER;
    Registry.OpenKey('Software\SysIT\Nails4You', true);

    Test := Registry.ReadString('Mandant') ;
    
// except

 // end;
  finally
// Registry.free;
  end;

// finally
// regist.free;
// end;

end;