change:
$WADbSearch1->addComparisonFromEdit("StartDate","S_StartDate"," AND",">=",2);
$WADbSearch1->addComparisonFromEdit("StartDate","S_EndDate","AN D","<=",2);
to:
$WADbSearch1->addComparisonFromEdit("StartDate","S_StartDate"," AND",">=",2);
$WADbSearch1->addComparison("OrderDate","".((isset($_GET["S_EndDate"]))?WAQB_getEndDate($_GET["S_EndDate"]):"") ."","AND","<=",2);
if you continue to have a problem, send a copy of the search and results pages so i can look at the code in context.