asp.net 代码问题 一个问题！！


<td style="width: 816px; height: 98px" valign="top">
                    <asp:GridView ID="gvBookTaxis" runat="server" AutoGenerateColumns="False" CellPadding="4" ForeColor="#333333" GridLines="None"                        PageSize="5" Width="815px" OnRowDataBound="gvBookTaxis_RowDataBound" OnSelectedIndexChanged="gvBookTaxis_SelectedIndexChanged">
                        <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                        <Columns>
                            <asp:BoundField HeaderText="排名" />
                            <asp:BoundField DataField="bookBarCode" HeaderText="图书条形码" />
                            <asp:BoundField DataField="bookName" HeaderText="图书名称" />
                            <asp:BoundField DataField="bookType" HeaderText="图书类型" />
                            <asp:BoundField DataField="bookcase" HeaderText="图书书架" />
                            <asp:BoundField DataField="bookConcern" HeaderText="出版社" />
                            <asp:BoundField DataField="author" HeaderText="作者" />
                            <asp:BoundField DataField="price" HeaderText="图书定价" />
                            <asp:BoundField DataField="borrowSum" HeaderText="借阅次数" />
                        </Columns>
这个是我的代码
但是为什么有错误
错误显示：错误 22 “ASP.index_aspx”并不包含“gvBookTaxis_SelectedIndexChanged”的定义 F:\asp.net\TM\04\libraryManage\index.aspx 39 谢谢！