gridview to formview - formview not showing any data - asp.net

Question

I have a gridview where, if you select a row, it takes you to a formview where you can view details from that entry and edit the data. This worked when I had only one filter parameter, but I added another, and now the formview is showing up blank. Here's my code:
<asp:AccessDataSource ID="courseinfo" runat="server" DataFile="~/App_Data/courseinfo.mdb" SelectCommand="SELECT [prefix], [course_number], [title], [date_submitted] FROM [tableCourse]">
</asp:AccessDataSource>
<asp:AccessDataSource ID="courseinfo2" runat="server" DataFile="~/App_Data/courseinfo.mdb" FilterExpression="prefix='{0}' AND course_number='{1}'" SelectCommand="SELECT * FROM [tableCourse]">
<FilterParameters>
<asp:ControlParameter Name="prefix" ControlID="GridView1" PropertyName="SelectedValue" />
<asp:ControlParameter Name="course_number" ControlID="GridView1" PropertyName="SelectedValue" />
</FilterParameters>
</asp:AccessDataSource>
<asp:GridView ID="GridView1" runat="server" DataSourceID="courseinfo" DataKeyNames="prefix,course_number"
OnSelectedIndexChanged="GridView1_SelectedIndexChanged" AutoGenerateColumns="False"
CellPadding="8" ForeColor="#333333" GridLines="vertical" BorderWidth="1" BorderColor="#dddddd"
AllowPaging="true" AllowSorting="true" AutoGenerateSelectButton="true">
<RowStyle BackColor="#eeeeee" />
<Columns>
<asp:BoundField DataField="prefix" HeaderText="prefix" SortExpression="prefix" />
<asp:BoundField DataField="course_number" HeaderText="number" SortExpression="course_number" />
<asp:BoundField DataField="title" HeaderText="title" SortExpression="title" />
<asp:BoundField DataField="date_submitted" HeaderText="date submitted" SortExpression="date_submitted" />
</Columns>
<FooterStyle BackColor="black" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="black" ForeColor="White" HorizontalAlign="Center" />
<SelectedRowStyle BackColor="#c0c0e0" Font-Bold="True" ForeColor="#333333" />
<HeaderStyle BackColor="#000000" Font-Bold="True" ForeColor="#eeeeee" />
<EditRowStyle BackColor="#2461BF" />
<AlternatingRowStyle BackColor="White" />
</asp:GridView>
<asp:FormView ID="FormView1" runat="server" DefaultMode="Edit" DataSourceID="courseinfo2"
DataKeyNames="prefix,course_number" Width="100%">
Of course the formview is complete but it contains a lot of code so I didn't include that here, although if anyone wants to see it, I can post it.

Answer 1

You can change your control parameters as follows reason being since you have multiple datakeynames, you cant have selected value as property of both. This should work however:
<asp:ControlParameter Name="prefix" ControlID="GridView1" PropertyName="SelectedDataKey.Values[prefix]" Type="String" />
<asp:ControlParameter Name="course_number" ControlID="GridView1" PropertyName="SelectedDataKey.Values[course_number]" Type="Int32" />