Gridview Error on editing with dropdownlist - asp.net

Question

I have grid view with folowing complete code With Msaccess DB.I have used the decode function in sql query.When i press the edit button on grid view it shows folowing error
"DropDownList2' has a SelectedValue which is invalid because it does not exist in the list of items.
Parameter name: value"
My SQL Data source code is below
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:DataConnectionString2 %>"
DeleteCommand="DELETE FROM [EMAILS] WHERE [ID] = ?" InsertCommand="INSERT INTO [EMAILS] ([Email], [FULLNAME],[FLAG]) VALUES (?, ?, ?)"
ProviderName="<%$ ConnectionStrings:DataConnectionString2.ProviderName %>" SelectCommand="SELECT ID, Email, FULLNAME, switch(FLAG = 1, 'Allowed', Flag = 0, 'Not Allowed') AS FLAG FROM EMAILS"
UpdateCommand="UPDATE [EMAILS] SET [Email] = ?, [FULLNAME] = ?,[FLAG] = ? WHERE [ID] = ?">
<DeleteParameters>
<asp:Parameter Name="ID" Type="Int32" />
</DeleteParameters>
<UpdateParameters>
<asp:Parameter Name="Email" Type="String" />
<asp:Parameter Name="FULLNAME" Type="String" />
<asp:Parameter Name="FLAG" Type="Int32" />
<asp:Parameter Name="ID" Type="Int32" />
</UpdateParameters>
<InsertParameters>
<asp:Parameter Name="Email" Type="String" />
<asp:Parameter Name="FULLNAME" Type="String" />
<asp:Parameter Name="FLAG" Type="Int32" />
</InsertParameters>
</asp:SqlDataSource>
And Grid View Code is bellow
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" AllowSorting="True"
AutoGenerateColumns="False" BackColor="White" BorderColor="#CC9966" BorderStyle="None"
BorderWidth="1px" CellPadding="4" DataKeyNames="ID" DataSourceID="SqlDataSource1"
HorizontalAlign="Center" Width="821px" EmptyDataText="No Emails Found">
<RowStyle BackColor="White" Font-Names="Arial" Font-Size="Small" ForeColor="Black" />
<Columns>
<asp:CommandField ButtonType="Button" ShowEditButton="True" ShowSelectButton="True" ShowDeleteButton="True" />
<asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True"
SortExpression="ID" Visible="False" />
<asp:BoundField DataField="Email" HeaderText="Email" SortExpression="Email" />
<asp:BoundField DataField="FULLNAME" HeaderText="Full Name" SortExpression="FULLNAME" />
<asp:TemplateField HeaderText="Flag" SortExpression="FLAG">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList2" runat="server" SelectedValue="<%# Bind('FLAG') %>" AppendDataBoundItems="True">
<asp:ListItem Value="1">Allowed</asp:ListItem>
<asp:ListItem Value="0">Not Allowed</asp:ListItem>
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("FLAG") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<FooterStyle BackColor="#FFFFCC" ForeColor="#330099" />
<PagerStyle BackColor="#FFFFCC" ForeColor="#330099" HorizontalAlign="Center" />
<SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="#663399" />
<HeaderStyle BackColor="#990000" Font-Bold="True" Font-Names="Arial" Font-Size="Small"
ForeColor="#FFFFCC" HorizontalAlign="Center" />
<EmptyDataRowStyle BackColor="#804000" Font-Names="Arial" Font-Size="Small" ForeColor="White" />
</asp:GridView>
Please tell me what possible error is here

Answer 1

Check weather the value in Field flag of the row you are trying to edit, is available in the DropDownList in EditItemTemplate
And try removing AppendDataBoundItems="True" in DropDownList in EditItemTemplate