checkbox - Select checkboxes all only works once?

Im using a checkbox in the table header to select (or unselect) all checkboxes in that column. Im new to JQuery.

Code in script (Run from inside $(document).ready(function() {)....

$('#check_all').click( function() {
$('input', oTable.fnGetNodes()).attr('checked',this.checked);
} );

This code works perfectly but only once! I can click it and select all AND then i can click it and it will unselect all. However from then on i click it and nothing happens.

When i chuck a console.log("Check event hit"); into the script it fires every time.. yet it only updates the checkboxes for the first check and uncheck operations.

Any thoughts?

Matt