Microsoft JScript runtime error when switching to compat mode (to test from IE9 to IE8)

Hi have i coded the below correctly as i wish to stop all sorting on all columns, it works fine in IE9 and none of the columns are sortable as expected. But i get a "Microsoft JScript runtime error: Unable to get value of the property 'aTargets': object is null or undefined" when i run in compatibility mode to see if works ok in IE8 mode. Unfortunately the company i work for use IE8 at the moment :/

 "aaSorting": [], //Remove all initial sorting (prevents the edit column being sorted initially).
            "aoColumnDefs": [
                       { "bSortable": false, "aTargets": [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11] }, //dont allow Sorting When clicking on the header.
                    ],