title: Problem in populating gridview from stored procedure
body: <p>I have a Gridview which I'm populating from a Stored Procedure which accepts 3 parameters. First parameter gets its value from a form variable Request.Form["uid"], second and third get its value from DropDownLists SelectedValue property. Second and third parameter should accept NULL if nothing is selected from DropDownLists. I have also set the ConvertEmptyStringToNull property of the parameters to true. 
  The Gridview is still not populating. But when I pass parameters manually and execute the stored procedure from SQL Server Management Studio as well as Visual Studio's test query window, it works fine.</p>
  
  <p>My SQLDataSource for the Gridview looks like this:</p>
  
  <pre><code>&lt;asp:SqlDataSource ID="SqlGVDownloadHistory" CancelSelectOnNullParameter="false" runat="server" ConnectionString="&lt;%$ ConnectionStrings:xxx %&gt;"
              SelectCommand="spDHR" SelectCommandType="StoredProcedure"&gt;
              &lt;SelectParameters&gt;
                  &lt;asp:FormParameter FormField="uid" Name="UIDUser" Type="String" /&gt;
                  &lt;asp:ControlParameter ControlID="ddlSelectDocument" Name="FileName"
                      PropertyName="SelectedValue" Type="String" ConvertEmptyStringToNull="true" /&gt;
                  &lt;asp:ControlParameter ControlID="ddlSelectCCO" Name="UIDSelect" PropertyName="SelectedValue"
                      Type="String" ConvertEmptyStringToNull="true" /&gt;
              &lt;/SelectParameters&gt;
          &lt;/asp:SqlDataSource&gt;
  </code></pre>
  
  <p>Please help!!</p>