change line 14 of the results page:
if ((isset($_GET["Search_x"]) && $_GET["Search_x"] != "")) {
to:
if ((isset($_GET["Search_x"]) && $_GET["Search_x"] != "" && ((isset($_GET["S_MS1"]) && $_GET["S_MS1"] != "") || (isset($_GET["S_MS2"]) && $_GET["S_MS2"] != "") || (isset($_GET["S_MS3"]) && $_GET["S_MS3"] != "")))) {