newbbでこんなエラーが出てしまうのですが、どうしたら良いか教えてください。

Notice [PHP]: Undefined offset: 1 in file modules/newbb/class/NewbbViewForm.class.php line 451
Notice [PHP]: Undefined offset: 1 in file modules/newbb/class/NewbbViewForm.class.php line 453
Notice [PHP]: Undefined offset: 1 in file modules/newbb/class/NewbbViewForm.class.php line 451
Notice [PHP]: Undefined offset: 1 in file modules/newbb/class/NewbbViewForm.class.php line 453
Notice [PHP]: Only variables should be assigned by reference in file modules/newbb/class/NewbbViewForm.class.php line 473
Notice [PHP]: Only variables should be assigned by reference in file modules/newbb/class/NewbbViewForm.class.php line 474
Notice [PHP]: Only variables should be assigned by reference in file modules/newbb/class/NewbbViewForm.class.php line 475