$(document).ready(function() {
	jQuery("#table1").jqGrid({
	url:'server.htm?ACTION2=JSON_LISTING&TABLENAME=testing',
	datatype: "json",
	colNames:['testTxt','update date','Login','number_dba','boolean1','Last Updated On','Created By'],
	colModel:[
	{name:'testTxt',index:'testTxt',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'update_date',index:'update_date',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'Login',index:'Login',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'Number',index:'Number',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'boolean1',index:'boolean1',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'MOD_DATE',index:'MOD_DATE',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}},
	{name:'ADD_BY',index:'ADD_BY',searchoptions:{sopt:['eq','ne','lt','le','gt','ge']}}	],
			rowNum:10,
		mtype:'POST',
		multiselect: true,
		rowList:[10,20,30],
		pager: '#pager1',
		loadComplete: doWhenGridFullyLoaded,
		gridview: true,
		autowidth: true, 
		toolbar:[true,"top"]
		}).navGrid('#pager1',
			{
				edit:false,add:false,del:false,search:true,refresh:false
			},
			{multipleSearch:true}
			);
		$("#t_table1").append("<a href='#' class='customize_icon ui'>&nbsp;&nbsp;Add New</a>");
		$("#t_table1").append("<a href='#' class='customize_icon_del'>&nbsp;&nbsp;Delete</a>");
});

Since I have enabled multipleSearch, but it still doesn't work for me. Anyone can point what I have done wrong.