my apologies, there is a missing quote at the end:
$PP_DirectPayment_optional[0][$nextIndex] = "SH_Name";
$PP_DirectPayment_optional[1][$nextIndex] = "".((isset($_POST["shipping_firstname"]))?$_POST["shipping_firstname"]:"") ." ".((isset($_POST["shipping_lastname"]))?$_POST["shipping_lastname"]:"") ."";