Datatable state save

Hi i have only one datatable in a page for which i need to save the state. I am able to change the state with the below code

     $('#details').dataTable( {
            "bPaginate": true,
            "bJQueryUI": true,
             "bAutoWidth": false,
                     "bStateSave": true,
                    "order": [ 5, 'desc' ],
            "sPaginationType": "full_numbers",
            "sDom": '<"right"l><"right"fp>rt<"bottom"i><"clear">'
      } );

Actually i was able to save state with just "bStateSave": true But my problem is the saved state is persisting among different user logins which i dont want to happen. Hence i introduced the below code

                      "fnStateSave": function (oSettings, oData) {
                           localStorage.setItem( 'DataTables_'+userid, JSON.stringify(oData) );
                       },
                     "fnStateLoad": function (oSettings) {
                           return JSON.parse( localStorage.getItem('DataTables_'+userid) );
                      }

in a view that for each user i will have different places in localstorage with a key 'DataTables_'+userid. But i am wrong. The above code is ignored and still whatever state saved for previous user comes when the new user logsin and vice a versa.

After going thru some posts i had included "bServerSide": true. Now i get the below error

"DataTables warning: table id=details - Invalid JSON response. For more information about this error, please see http://datatables.net/tn/1"

My final code is given below

     $('#details').dataTable( {
            "bPaginate": true,
            "bJQueryUI": true,
             "bAutoWidth": false,
            "bServerSide": true,
                     "bStateSave": true,
                     "fnStateSave": function (oSettings, oData) {
                           localStorage.setItem( 'DataTables_'+path, JSON.stringify(oData) );
                       },
                     "fnStateLoad": function (oSettings) {
                           return JSON.parse( localStorage.getItem('DataTables_'+path) );
                      },
                    "order": [ 5, 'desc' ],
            "sPaginationType": "full_numbers",
            "sDom": '<"right"l><"right"fp>rt<"bottom"i><"clear">'
      } );

I am completely new for jquery and datatables. Please let me know where i am going wrong and what needs to be done. My requirement is to save datatable state for each user seperately in localstorage.