jQuery Grid Plugin - jqGrid

My grid is to load about 500 records at once (load all data, no paging).

It works fine in firefox and IE 8, but the event "loadComplete" doesn't happen in IE 7 and there's a error "t.p.colModel[...]name is null or not an object ". Plz let me know how I can fix it !

Here's the code :

    var gridAssignedTestCase = $("#grid_assigned_test_case").jqGrid({
        url: Ts.CONTEXT_PATH_NS + '/loadAssignedTestCaseOfTask.do',
        colNames:[Ts.Label.ID, Ts.Label.TestScenario, Ts.Label.Requirement, Ts.Label.FlowID,  Ts.Label.Status, Ts.Label.Environment, Ts.Label.Time, '', ''],
        colModel:[  {name:'concreteTestCaseId', key:true, index:'concreteTestCaseId', width:70, align:"center", stype:'none', sortable:true},
                    {name:'testScenario',index:'testScenario', stype:'none', width:220, sortable:false},
                    {name:'requirementName',index:'requirementName', width:190, stype:'none', sortable:true},
                    {name:'flowId',index:'flowId',width:70, align:"right", sorttype:"int", stype:'none', sortable:true},    
                    {name:'executionStatusId',index:'executionStatusId',width:75, align:"left", stype:'none',hidden: false, sortable:false,
                        formatter:"select",editable: false, edittype:"select",editoptions:{value:"81:Not Test; 82:Passed; 83:Failed; 84:NA; 85:Blocked"}},
                    {name:'environmentCode',index:'environmentCode',width:230, align:"left", sortable:false},
                    {name:'estimatedDuration',index:'estimatedDuration',align:"right",width:40, sortable:false, stype:'none'},
                    {name:'testCaseTaskId',index:'testCaseTaskId',align:"right",width:0, sortable:false, stype:'none', hidden: true},
                    {name:'usageExecutionStatus',index:'usageExecutionStatus',align:"right",width:0, sortable:false, stype:'none', hidden: true} ],                         
        height: 440,
        cellEdit : true,
        rowNum : 9999,
        postData: {'id' : id},
        loadComplete: function(tc){
            writeTotalEstimateTime();
        }
        caption: Ts.Label.AssignedTestCaseList
    });