求解 EXTJS 3.0 这个错误：Uncaught TypeError: Cannot set property 'width' of undefined

我在做前台是用了多重表头，后来就出现了这个“Uncaught TypeError: Cannot set property 'width' of undefined”，而且每次reload那个store的时候就会出现，一直显示laodMask的情况，不知道为什么，google和baidu也查了，请高人解答

//自定义双重表头
MyGridView = Ext.extend(Ext.grid.GridView, {
        renderHeaders : function() {
            var cm = this.cm, ts = this.templates;
            var ct = ts.hcell, ct2 = ts.mhcell;
            var cb = [], sb = [], p = {}, mcb = [];
            for (var i = 0, len = cm.getColumnCount(); i < len; i++) {
                p.id = cm.getColumnId(i);
                p.value = cm.getColumnHeader(i) || "";
                p.style = this.getColumnStyle(i, true);
                if (cm.config[i].align == 'right') {
                    p.istyle = 'padding-right:16px';
                }
                cb[cb.length] = ct.apply(p);
                if (cm.config[i].mtext)
                    mcb[mcb.length] = ct2.apply({
                                value : cm.config[i].mtext,
                                mcols : cm.config[i].mcol,
                                mwidth : cm.config[i].mwidth
                            });
            }
            var s = ts.header.apply({
                        cells : cb.join(""),
                        tstyle : 'width:' + this.getTotalWidth() + ';',
                        mergecells : mcb.join("")
                    });
            return s;
        }
    });

viewConfig = {
templates : {
header : new Ext.Template(
            ' <table border="0" cellspacing="0" cellpadding="0" style="{tstyle}">',
            ' <thead> <tr class="x-grid3-hd-row">{mergecells} </tr>'
                    + ' <tr class="x-grid3-hd-row">{cells} </tr> </thead>',
            " </table>"),
            mhcell : new Ext.Template(
            ' <td class="x-grid3-header" colspan="{mcols}" style="width:{mwidth}px;"> <div align="center">{value}</div>',
            " </td>")
}
};

var activeDriverReport_grid= new Ext.grid.GridPanel( {
id:'activeDriverReport_grid',
region : 'center',
loadMask :true,
split : true,
columnLines : true,
layout:'fit',
store : activeDriverReport_store,
cm : activeDriverReport_cm,
sm: centersm,
viewConfig : {forceFit : false},
view : new MyGridView(viewConfig),
autoScroll: true,
height:600,
width:200
}

如果还需要什么代码的话可以加我qq：670500167
请高人解答。

具体问题图片在百度知道里面有，搜：“Uncaught TypeError: Cannot set property 'width' of undefined"能找到

--------------------编程问答-------------------- 都遇见同一个问题不知楼主怎么解决的 --------------------编程问答-------------------- 楼主是怎么解决的

补充：Java ,  Web 开发