Code
<system.web.extensions>
        <scripting>
            <webServices>
        <jsonSerialization maxJsonLength="2000000">
            <add name="DataTableConverter" type="Ext.Converters.DataTableConverter,Ext"/>
                    </converters>
                </jsonSerialization>
                <profileService enabled="false" readAccessProperties="propertyname1,propertyname2" writeAccessProperties="propertyname1,propertyname2"/>
            </webServices>
            <scriptResourceHandler enableCompression="true" enableCaching="true"/>
        </scripting>
    </system.web.extensions>

Code
 public class DataTableConverter : JavaScriptConverter
    {
        public DataTableConverter()
        {
            this._supportedTypes = new ReadOnlyCollection<Type>(new Type[] { typeof(DataTable) });
        }
        public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
        {
            throw new NotSupportedException();
        }

        public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
        {
            DataTable table = obj as DataTable;
            if (table == null)
            {
                throw new ArgumentException("obj");
            }
            IDictionary<string, object> dictionary = new Dictionary<string, object>(2);

            //如果需要分页，则把总行数保存到这个扩展属性中。
            if (table.ExtendedProperties["TotalCount"] != null)
            {
                dictionary["TitleCount"] = int.Parse(table.ExtendedProperties["TotalCount"].ToString());
            }
            else
            {
                dictionary["TitleCount"] = table.Rows.Count;
            }

            if (table.Rows.Count > 0)
            {
                DataRow[] rowArray = new DataRow[table.Rows.Count];
                for (int j = 0; j < rowArray.Length; j++)
                {
                    rowArray[j] = table.Rows[j];
                }
                dictionary["Rows"] = rowArray;
                return dictionary;
            }

            dictionary["Rows"] = new string[0];
            return dictionary;
        }
        private ReadOnlyCollection<Type> _supportedTypes;

        public override IEnumerable<Type> SupportedTypes
        {
            get { return this._supportedTypes; }
        }
    }

Code
SFCity.IMManageGrid = function(config){
    var store = new Ext.data.Store({
        proxy : new Ext.data.HttpProxy({url:'Services/IMLog.asmx/MyIMLog',isWebService:true}),
        reader : new Ext.data.JsonReader({
            root:'Rows',
            totalProperty:'TotalCount',
            fields:['FID','FIpAddress','FUserName','FSource','FSalesman','FPostDate','FSign']
        }),
        listeners : {beforeload : this.onBeforeLoad,scope : this},
        sortInfo:{field:'FPostDate',direction:'DESC'},
        remoteSort:true
    });
    var sm = new Ext.grid.CheckboxSelectionModel();
    var dataColumns = new Ext.grid.ColumnModel([
        sm,
        {header: "IP地址",dataIndex:'FIpAddress',sortable: true,width:130},
        {header: "会员ID",dataIndex:'FUserName',sortable: true,width:130},
        {header: "来源",dataIndex:'FSource',sortable: true,width:130},
        {header: "时间",dataIndex:'FPostDate',renderer:Ext.util.Format.dateTime, sortable: true,align:'center',width:150},
        {header: "重要",dataIndex:'FSign', sortable: true,align:'center',width:120,renderer:function(value){return value?'是':'否';}}
    ]);

    this.pagingBar= new Ext.PagingToolbar({
        pageSize: 25,
        store: store,
        displayInfo: true,
        autoShow : true,
        displayMsg:'当前显示 {0} - {1} 条记录/共 {2} 条记录',
        refreshText:'刷新',
        beforePageText:'第',
        afterPageText:'页/共 {0} 页',
        firstText:'第一页',
        lastText:'最后一页',
        nextText:'下一页',
        prevText:'上一页',
        emptyMsg:"暂无记录"         
    });
    //
    config = config||{};
    config = Ext.apply(config,{
        store:store,
        cm:dataColumns,
        sm:sm,
        loadMask:{msg:'正在加载数据中，请稍候……'},
        title:'IM聊天记录',
        frame:true,
        trackMouseOver:true,
        listeners :{rowdblclick : this.ondblClick ,scope : this},
        bbar: this.pagingBar
    });
    this.config = config;
    SFCity.IMManageGrid.superclass.constructor.call(this, config);
    this.refresh();  
}
Ext.extend(SFCity.IMManageGrid, Ext.grid.GridPanel, {
    doQuery : function(){
        this.refresh();
    },
    refresh : function(){
        this.pagingBar.cursor = 0;
        this.getStore().load({params:{start:this.pagingBar.cursor, limit:this.pagingBar.pageSize}});
    }
});