“DropDownList1”有一个无效 SelectedValue，因为它不在项目列表中。

下面的代码老是提示
“DropDownList1”有一个无效 SelectedValue，因为它不在项目列表中。
参数名: value
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。

异常详细信息: System.ArgumentOutOfRangeException: “DropDownList1”有一个无效 SelectedValue，因为它不在项目列表中。
参数名: value

我是想把depid数字显示为部门编号,但是不知道为什么老是提示上面的错误,搞不清了,大家帮忙看看


<asp:FormView ID="FormView1" runat="server" AllowPaging="True" DataKeyNames="ID"
DataSourceID="SqlDataSource1">
<EditItemTemplate>
ID:
<asp:Label ID="IDLabel1" runat="server" Text='<%# Eval("ID") %>'></asp:Label><br />
UserName:
<asp:TextBox ID="UserNameTextBox" runat="server" Text='<%# Bind("UserName") %>'></asp:TextBox><br />
PassWD:
<asp:TextBox ID="PassWDTextBox" runat="server" Text='<%# Bind("PassWD") %>'></asp:TextBox><br />
depname:
<asp:TextBox ID="depnameTextBox" runat="server" Text='<%# Bind("depname") %>'></asp:TextBox><br />
depid:
<asp:TextBox ID="depidTextBox" runat="server" Text='<%# Bind("depid") %>'></asp:TextBox>
<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource2" SelectedValue='<%# Bind("depid") %>'
DataTextField="depid" DataValueField="depid" >
</asp:DropDownList><br />
<asp:LinkButton ID="UpdateButton" runat="server" CausesValidation="True" CommandName="Update"
Text="更新"></asp:LinkButton>
<asp:LinkButton ID="UpdateCancelButton" runat="server" CausesValidation="False" CommandName="Cancel"
Text="取消"></asp:LinkButton>
</EditItemTemplate>
<InsertItemTemplate>
UserName:
<asp:TextBox ID="UserNameTextBox" runat="server" Text='<%# Bind("UserName") %>'>
</asp:TextBox><br />
PassWD:
<asp:TextBox ID="PassWDTextBox" runat="server" Text='<%# Bind("PassWD") %>'>
</asp:TextBox><br />
depname:
<asp:TextBox ID="depnameTextBox" runat="server" Text='<%# Bind("depname") %>'>
</asp:TextBox><br />
depid:
<asp:TextBox ID="depidTextBox" runat="server" Text='<%# Bind("depid") %>'>
</asp:TextBox><br />
<asp:LinkButton ID="InsertButton" runat="server" CausesValidation="True" CommandName="Insert"
Text="插入">
</asp:LinkButton>
<asp:LinkButton ID="InsertCancelButton" runat="server" CausesValidation="False" CommandName="Cancel"
Text="取消">
</asp:LinkButton>
</InsertItemTemplate>
<ItemTemplate>
ID:
<asp:Label ID="IDLabel" runat="server" Text='<%# Eval("ID") %>'></asp:Label><br />
UserName:
<asp:Label ID="UserNameLabel" runat="server" Text='<%# Bind("UserName") %>'></asp:Label><br />
PassWD:
<asp:Label ID="PassWDLabel" runat="server" Text='<%# Bind("PassWD") %>'></asp:Label><br />
depname:
<asp:Label ID="depnameLabel" runat="server" Text='<%# Bind("depname") %>'></asp:Label><br />
depid:
<asp:Label ID="depidLabel" runat="server" Text='<%# Bind("depid") %>'></asp:Label><br />
<asp:LinkButton ID="EditButton" runat="server" CausesValidation="False" CommandName="Edit"
Text="编辑">
</asp:LinkButton>
<asp:LinkButton ID="DeleteButton" runat="server" CausesValidation="False" CommandName="Delete"
Text="删除">
</asp:LinkButton>
<asp:LinkButton ID="NewButton" runat="server" CausesValidation="False" CommandName="New"
Text="新建">
</asp:LinkButton>
</ItemTemplate>
</asp:FormView>
   <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConflictDetection="CompareAllValues"
ConnectionString="<%$ ConnectionStrings:jbwebschoolConnectionString %>" DeleteCommand="DELETE FROM [FT_User] WHERE [ID] = @original_ID"
InsertCommand="INSERT INTO [FT_User] ([UserName], [PassWD], [depname], [depid]) VALUES (@UserName, @PassWD, @depname, @depid)"
OldValuesParameterFormatString="original_{0}" SelectCommand="SELECT [ID], [UserName], [PassWD], [depname], [depid] FROM [FT_User]"
UpdateCommand="UPDATE [FT_User] SET [UserName] = @UserName, [PassWD] = @PassWD, [depname] = @depname, [depid] = @depid WHERE [ID] = @original_ID">
<DeleteParameters>
<asp:Parameter Name="original_ID" Type="Int32" />
</DeleteParameters>
<UpdateParameters>
<asp:Parameter Name="UserName" Type="String" />
<asp:Parameter Name="PassWD" Type="String" />
<asp:Parameter Name="depname" Type="String" />
<asp:Parameter Name="depid" Type="Int32" />
<asp:Parameter Name="original_ID" Type="Int32" />
</UpdateParameters>
<InsertParameters>
<asp:Parameter Name="UserName" Type="String" />
<asp:Parameter Name="PassWD" Type="String" />
<asp:Parameter Name="depname" Type="String" />
<asp:Parameter Name="depid" Type="Int32" />
</InsertParameters>
</asp:SqlDataSource>
<asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:jbwebschoolConnectionString %>"
SelectCommand="SELECT [depid], [depname], [deptype], [depnumber] FROM [dep]"></asp:SqlDataSource>