Dear Paul,
Ok I manage to solve the table name issue as below. The problem now is that each time I add few rows and submit it shows the length is just 1. So how to overcome this?

function checkRows(form) {
//$(form).validate().resetForm();
alert("Length : "+$('table.dynatable tbody tr', form).length);
if ($('table.dynatable tbody tr', form).length > 2) {
alert("Call setup multiple row");

}
}