调试易

问题：点击grid中更换按钮后ie8执行成功，正确返回并跳出正确的提示框，chrome执行则跳出错误提示信息，firefox没有任何提示信息，请高手解决
代码
    <script type="text/javascript" src="../js/jq.js"></script>
    <script language="javascript" type="text/javascript">
        function showchange(itemid, zgbm) {
                $.ajax({
                    //要用post方式     
                    type: "Post",
                    //方法所在页面和方法名
                    url: "LBChangeAdd.aspx/ChangeItem",
                    data: "{itemid:"+itemid+",zgbm:"+zgbm+"}",  
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function(data) {
                        //返回的数据用data.d获取内容     
                        alert(data.d);
                    },
                    error: function(err) {
                        alert("出错了:"+err);
                    }
                });     
        }
</script><asp:GridView id="grid" runat="server" AllowPaging="True" 
            Width="100%" Font-Size="Small"
            AutoGenerateColumns="False"   EmptyDataText="没有记录"
            OnPageIndexChanging="grid_PageIndexChanging" CellPadding="4" 
            ForeColor="#333333"  onrowdatabound="grid_RowDataBound" 
                >
            <FooterStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
            <RowStyle BackColor="#E3EAEB"  HorizontalAlign="Center" VerticalAlign="Middle"/>
            <columns>
<%--                      <asp:BoundField DataField="hidecode" headertext="hidecode" 
                    sortexpression="hidecode"  >
                    <ItemStyle CssClass="hidden"  />
                    <HeaderStyle CssClass="hidden" />
                </asp:BoundField>--%>
                <asp:ButtonField Text="更换"  />                <asp:BoundField DataField="itemid" headertext="itemid" 
                    sortexpression="itemid"  >
                    <ItemStyle CssClass="hidden"  />
                    <HeaderStyle CssClass="hidden" />
                </asp:BoundField>
                 <asp:BoundField DataField="zgbm" headertext="zgbm" 
                    sortexpression="zgbm"  >
                    <ItemStyle CssClass="hidden"  />
                    <HeaderStyle CssClass="hidden" />
                </asp:BoundField>
                    <asp:boundfield datafield="名称" HeaderStyle-Wrap="false" headertext="名称" 
                        ItemStyle-Wrap="false" sortexpression="名称">
                        <HeaderStyle Wrap="False" />
                        <ItemStyle Wrap="False" />
                    </asp:boundfield>
                    <asp:boundfield datafield="计量单位" HeaderStyle-Wrap="false" headertext="计量单位" 
                        ItemStyle-Wrap="false" sortexpression="计量单位">
                        <HeaderStyle Wrap="False" />
                        <ItemStyle Wrap="False" />
                    </asp:boundfield>
                    <asp:boundfield datafield="领用时间" HeaderStyle-Wrap="false" 
                        headertext="领用时间" ItemStyle-Wrap="false" sortexpression="领用时间">
                        <HeaderStyle Wrap="False" />
                        <ItemStyle Wrap="False" />
                    </asp:boundfield>
                    <asp:boundfield datafield="数量" HeaderStyle-Wrap="false" headertext="数量" 
                        ItemStyle-HorizontalAlign="Right" ItemStyle-VerticalAlign="Middle" 
                        ItemStyle-Wrap="false" sortexpression="数量">
                        <HeaderStyle Wrap="False" /><ItemStyle HorizontalAlign="Right" VerticalAlign="Middle" Wrap="False"></ItemStyle>
                    </asp:boundfield>
                    <asp:boundfield datafield="规格" HeaderStyle-Wrap="false" headertext="规格" 
                        ItemStyle-HorizontalAlign="Right" ItemStyle-VerticalAlign="Middle" 
                        ItemStyle-Wrap="false" sortexpression="规格">
                        <HeaderStyle Wrap="False" /><ItemStyle HorizontalAlign="Right" VerticalAlign="Middle" Wrap="False"></ItemStyle>
                    </asp:boundfield>
                    
            </columns>
            
               <pagertemplate>
                        <table width="100%">
                          <tr>
                            <td style="text-align:left">
                            第<asp:Label id="lblPageIndex" runat="server" text='<%# ((GridView)Container.Parent.Parent).PageIndex + 1  %>' />页
                                共/<asp:Label id="lblPageCount" runat="server" text='<%# ((GridView)Container.Parent.Parent).PageCount  %>' />页 
                                <asp:linkbutton id="btnFirst" runat="server" causesvalidation="False" commandargument="First" commandname="Page" text="首页" />
                              <asp:linkbutton id="btnPrev" runat="server" causesvalidation="False" commandargument="Prev" commandname="Page" text="上一页" />
                             <asp:linkbutton id="btnNext" runat="server" causesvalidation="False" commandargument="Next" commandname="Page" text="下一页" />                          
                             <asp:linkbutton id="btnLast" runat="server" causesvalidation="False" commandargument="Last" commandname="Page" text="尾页" />                                            
                             <asp:textbox id="txtNewPageIndex" runat="server" width="20px" text='<%# ((GridView)Container.Parent.Parent).PageIndex + 1  %>' />
                             <asp:linkbutton id="btnGo" runat="server" causesvalidation="False" commandargument="-1" commandname="Page" text="GO" /><!-- here set the CommandArgument of the Go Button to '-1' as the flag -->
                             </td>
                          </tr>
                        </table>
                </pagertemplate>
           <PagerStyle BackColor="#E3EAEB" ForeColor="#000000" HorizontalAlign="Center" />
            <SelectedRowStyle BackColor="#C5BBAF" Font-Bold="True" ForeColor="#333333" />
            <HeaderStyle BackColor="#1C5E55" Font-Bold="True" ForeColor="White" />
            <EditRowStyle BackColor="#7C6F57" />
            <AlternatingRowStyle BackColor="White" />
        </asp:GridView> 后台代码
    [System.Web.Services.WebMethod]
    public static string ChangeItem(String itemid, String zgbm)
    {
        return "成功更换！"+itemid+"--"+zgbm;
    }    protected void grid_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            if (e.Row.RowState == DataControlRowState.Normal || e.Row.RowState == DataControlRowState.Alternate)
            {
                int i = 0;
                ((LinkButton)e.Row.Cells[0].Controls[0]).Attributes.Add("onclick", "javascript:showchange('" + e.Row.Cells[i+1].Text + "','" + e.Row.Cells[i + 2].Text + "')");
                
            }
        }
    }