Fixedheader not working properly

Ajith86

Whenever I include the fixed header, while scrolling down ,it losses it's fixed position goes up on to the starting of the window. Could anyone please tell me what is going wrong here.. Any fix for this issue ?
Please find below the code I m using
html part
[code]













[/code]

script
[code]
$.ajax({
type : "POST",
url : url,
data:MODEL,
success : function(data)
{
if (typeof ddTable == 'undefined')
{
ddTable=$('#ex_table').dataTable({
"aaData" : data.response,
"aoColumns" : [
{ "sTitle": "Col1", "bSortable": true},
{ "sTitle": "Col2", "bSortable": true },
{ "sTitle": "Col3", "bSortable": true },
{ "sTitle": "Col4", "bSortable": true},
{ "sTitle": "Col5", "bSortable": true },
{ "sTitle": "Col6","bSortable": true }],
"bFilter" : false,
"bLengthChange" : false,
"bPaginate" : true,
"bInfo" : true,
"iDisplayLength" : 5,
"fnFooterCallback": function ( nRow, aaData, iStart, iEnd, aiDisplay ) {}

});
}
else
{
ddTable.fnClearTable( 0 );
ddTable.fnAddData(data.response);
}
new FixedHeader( ddTable );
}
});
[/code]