ok this is the gridview code, bounded to filedatasource, while the dropdownlist inside the gridview's footer row is bounded to categorydatasource
<asp:SqlDataSource ID="FileDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:SiteSqlServer %>"
DeleteCommand="DELETE FROM File_TA WHERE File_ID = @File_ID"
<DeleteParameters>
<asp:Parameter Name="File_ID" />
</DeleteParameters>
</asp:SqlDataSource>
<asp:GridView ID="GridView_File" runat="server" AutoGenerateColumns="False" DataKeyNames="File_ID"
DataSourceID="FileDataSource" ShowFooter="True" style="table-layout: auto" AllowPaging="True" Width="920px">
<Columns>
<asp:CommandField ShowDeleteButton="True" ShowEditButton="True" />
<asp:TemplateField HeaderText="ID" SortExpression="File_ID">
<EditItemTemplate>
<asp:Label ID="Label_EditFileID" runat="server" Text='<%# Eval("File_ID") %>'></asp:Label>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label_FileID" runat="server" Text='<%# Bind("File_ID") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:Button ID="Button_AddFile" runat="server" Text="Add" CommandName="InsertFile" ValidationGroup="File" />
<asp:TextBox ID="TextBox_FileID" runat="server" Visible="False" Width="118px"></asp:TextBox>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Category" SortExpression="Category_Name">
<EditItemTemplate>
<asp:DropDownList ID="EditCategoryList" runat="server"
SelectedValue='<%# Bind("Category_ID") %>' DataSourceID="CategoryDataSource" DataTextField="Category_Name" DataValueField="Category_ID" Width="80px">
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("Category_Name","{0:f2}") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:DropDownList ID="CategoryList" runat="server" SelectedValue='<%# Bind("Category_ID") %>' DataSourceID="CategoryDataSource" DataTextField="Category_Name" DataValueField="Category_ID">
</asp:DropDownList>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="File Name" SortExpression="File_Name">
<EditItemTemplate>
<asp:TextBox ID="TextBox_EditFileName" runat="server" Text='<%# Bind("File_Name") %>' Width="100px" Enabled="False"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label3" runat="server" Text='<%# Bind("File_Name") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:TextBox ID="TextBox_FileName" runat="server" Width="100px" ReadOnly="True"></asp:TextBox>
<asp:Label ID="FileNameLabel" runat="server"></asp:Label>
</FooterTemplate>
<ItemStyle HorizontalAlign="Center" />
<FooterStyle Wrap="True" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Price" SortExpression="File_Price">
<EditItemTemplate>
<asp:TextBox ID="TextBox_EditPrice" runat="server" Text='<%# Bind("File_Price") %>' Width="80px"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredEditPrice" runat="server" ControlToValidate="TextBox_EditPrice"
Enabled="False" ErrorMessage="*" Text='<%# Eval("File_Price", "{0:N}") %>'></asp:RequiredFieldValidator>
</EditItemTemplate>
<ItemTemplate>
Rp.
<asp:Label ID="Label4" runat="server" Text='<%# Bind("File_Price", "{0:N}") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:TextBox ID="TextBox_FilePrice" runat="server" Width="80px"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredPrice" runat="server" ControlToValidate="TextBox_FilePrice" ErrorMessage="*" ValidationGroup="File"></asp:RequiredFieldValidator>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Description" SortExpression="File_Description">
<EditItemTemplate>
<asp:TextBox ID="TextBox_EditDescription" runat="server" Text='<%# Bind("File_Description") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label5" runat="server" Text='<%# Bind("File_Description") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:TextBox ID="TextBox_FileDescription" runat="server"></asp:TextBox>
</FooterTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Location" SortExpression="File_Location">
<EditItemTemplate>
<asp:FileUpload ID="Edit_Location" runat="server" />
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label6" runat="server" Text='<%# Bind("File_Location") %>'></asp:Label>
</ItemTemplate>
<FooterTemplate>
<asp:FileUpload ID="File_Location" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFileLocation" runat="server" ControlToValidate="File_Location"
ErrorMessage="*" ValidationGroup="File"></asp:RequiredFieldValidator>
</FooterTemplate>
</asp:TemplateField>
</Columns>
<FooterStyle HorizontalAlign="Center" Wrap="True" />
</asp:GridView>
i don't put any code behind for delete event
this one is a gridview which is bounded to category data source
<asp:GridView ID="GridView_FileCategory" runat="server" AutoGenerateColumns="False" DataKeyNames="Category_ID" DataSourceID="CategoryDataSource" ShowFooter="True">
<Columns>
<asp:CommandField ShowDeleteButton="True" ShowEditButton="True" />
<asp:TemplateField HeaderText="Category_ID" SortExpression="Category_ID">
<EditItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Eval("Category_ID") %>'></asp:Label>
</EditItemTemplate>
<FooterTemplate>
<asp:Button ID="Button_AddCategory" runat="server" CommandName="Insert" Text="Add" ValidationGroup="Category" />
<asp:TextBox ID="TextBox_CategoryID" runat="server" Visible="False"></asp:TextBox>
</FooterTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("Category_ID") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Category_Name" SortExpression="Category_Name">
<EditItemTemplate>
<asp:TextBox ID="TextBox_EditCategory" runat="server" Text='<%# Bind("Category_Name") %>'></asp:TextBox>
</EditItemTemplate>
<FooterTemplate>
<asp:TextBox ID="TextBox_CategoryName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredCategory" runat="server" ControlToValidate="TextBox_CategoryName" ErrorMessage="*" ValidationGroup="Category"></asp:RequiredFieldValidator>
</FooterTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("Category_Name") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Category_Description" SortExpression="Category_Description">
<EditItemTemplate>
<asp:TextBox ID="TextBox_EditCategoryDescription" runat="server" Text='<%# Bind("Category_Description") %>'></asp:TextBox>
</EditItemTemplate>
<FooterTemplate>
<asp:TextBox ID="TextBox_CategoryDescription" runat="server"></asp:TextBox>
</FooterTemplate>
<ItemTemplate>
<asp:Label ID="Label3" runat="server" Text='<%# Bind("Category_Description") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="CategoryDataSource" runat="server" ConnectionString="<%$ ConnectionStrings:SiteSqlServer %>"
DeleteCommand="DELETE FROM [File_TA_Category] WHERE [Category_ID] = @Category_ID"
<DeleteParameters>
<asp:Parameter Name="Category_ID" Type="Int32" />
</DeleteParameters>
</asp:SqlDataSource>
the error message is exactly the same as title...that's all... that's why i dun understand either