Pdf and xls not working on data table

Pdf and xls not working on data table....
i am using the following code
"sDom": 'T<"clear">lfrtip',
"aButtons": [

"xls",
{
"sExtends": "pdf",
"sPdfSize": "letter"
}

]

it is creating only buttons but there is no action while i clicking...
can anyone help me please...