Well, I have met the same problem. My code is bellow:

 <div dojoType="dojo.data.ItemFileReadStore"
  jsId="jsonStore"
  url="../../Dojo/dijit/tests/_data/countries.json"
  ></div>
 <div dojoType="dojo.data.ItemFileReadStore"
  jsId="jsonStore2"
  url="../JSON/getNews.json.php"
  ></div>
 <div dojoType="dojo.data.ItemFileReadStore"
  jsId="jsonStore3"
  url="../JSON/json.txt"
  ></div>
 <span dojoType="dojox.grid.data.DojoData"
  jsId="dataModel"
  rowsPerPage="10"
  store="jsonStore2"
 >
 </span>
 <div id="grid2" dojoType="dojox.Grid" elasticView="2"
  model="dataModel" structure="layoutCountries">
 </div>

I found that , no matter which "jsonStore" I choose , it goes well on FireFox. But once I put it on IE , with "jsonStore2" , use ".php" to support the json data , it just send an error. When I'm using dijit.form.FilteringSelect , I've met the same problem already .

"dojo.data.ItemFileReadStore" can't go well on IE if I use ".php" to support the "json" data.

I copied your code above, changed the references to the aolcdn css files and the .js files to my local path, and used the states.json file below. The bottom grid, labeled "Programmatic Grid", displays fine in FF2 and IE7.

        Test dojox.Grid Basic
        
        
        @import "js/dojotoolkit/dojox/grid/_grid/tundraGrid.css";
        @import "js/dojotoolkit/dijit/themes/tundra/tundra.css";
        @import "js/dojotoolkit/dojo/resources/dojo.css"

                body {
                        font-size: 0.9em;
                        font-family: Geneva, Arial, Helvetica, sans-serif;
                }
                .heading {
                        font-weight: bold;
                        padding-bottom: 0.25em;
                }
                               
                #grid1 {
                        border: 1px solid #333;
                        width: 35em;
                        height: 30em;
                }
                                .heading1 {
                                                font-weight: bold;
                                                padding-bottom: 0.25em;
                                }

                                #my_grid {
                                                border: 1px solid #333;
                                                width: 50em;
                                                height: 30em;
                                }

        
        

        
            dojo.require("dojo.data.ItemFileReadStore");
                        dojo.require("dojox.grid.Grid");
                        dojo.require("dojox.grid._data.model");
                        dojo.require("dojo.parser");
   
                        // a grid view is a group of columns.
                        var view1 = {
                                        cells: [[
                                                                {name: 'Abbreviation', width: "10%", field: "abbreviation"},
                                                                {name: 'StateName', width: "30%", field: "name"},
                                                                {name: 'Label', width: "60%", field: "label"}
                                          ]
                                        ]
                        };
                        // a grid layout is an array of views.
                        var layout = [ view1 ];
                
                
                         dojo.addOnLoad(function(){
                                // a grid layout is an array of views.
                                var my_view = {
                                        cells: [[
                                                        {name: 'StateName', width: "50%", field: "name"},
                                                        {name: 'Abbreviation', width: "50%", field: "abbreviation"}
                                          ]
                                        ]
                                };
                                // a grid layout is an array of views.
                                var my_layout = [ my_view ];
                                var my_store = new dojo.data.ItemFileReadStore({jsId: 'my_jsonStore', url: 'states.json'});
                                var my_model = new dojox.grid.data.DojoData(null, my_store,{jsId: 'my_model', rowsPerPage: 20, query: { name: '*' }});
                                var my_grid = new dojox.Grid({"id": "my_grid",model: my_model,structure : my_layout,"class": "tundra",rowsPerPage: 20});
                                dojo.byId("gridContainer").appendChild(my_grid.domNode);
                                my_grid.render();
                         });
                
                
                        function fillNewData(){
                                /* filter the message list to messages in this folder */
                                // set new model
                                var my_store = new dojo.data.ItemFileReadStore({jsId: 'my_store', url: 'states.json'});

                                var newModel = new dojox.grid.data.DojoData();
                                newModel.rowsPerPage = 20;
                                newModel.store = my_store;
                                newModel.query = {
                                        name: "N*"
                                };
                                newModel.clientSort = true;
                                myGrid.setModel(newModel);
                                myGrid.setStructure(layout);
                        }

                        function changeStructure(){
                                /* filter the message list to messages in this folder */
                                var new_view = {
                                        cells: [[
                                                        {name: 'Abbreviation', width: "10%", field: "abbreviation"},
                                                        {name: 'StateName', field: "name"}
                                          ]
                                        ]
                                };
                                // a grid layout is an array of views.
                                var new_layout = [ new_view ];
                                myGrid.setStructure(new_layout);
                        }
        


                
Simple Grid
        

        
        

        
        


                
                  
                
                
                


                
Programatic Grid
        

states.json

{identifier:"abbreviation",
items: [
        {name:"Alabama", label:"Alabama",abbreviation:"AL"},
        {name:"Alaska", label:"Alaska",abbreviation:"AK"},
        {name:"American Samoa", label:"American Samoa",abbreviation:"AS"},
        {name:"Wyoming", label:"Wyoming",abbreviation:"WY"}
]}

If your states.json file has a trailing comma after the last {...} entry, IE will not like it.