DataSource Controls :: GridView - Control Parameter Error Using Oracle SQLDataSource

I have an user control placed on a content page. The content correctly receives the session variables. In the user control I have the following

1. The pageload fires and the text box is correctly set.

<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
if (Session["app_id"] != null)
{
txtAppId.Text = Session["app_id"].ToString();
}
</script>

2. I have datagrid in the usercontrol which has a binding variable tied to a control parameters as follows

<asp:SqlDataSource ID="SqlDataSourceMain" runat="server"
ConnectionString="Myconnectionstring"
ProviderName="MyProvider" SelectCommand="select
last_name,first_name
from applications
where (id = to_number(:pAppId))">
<SelectParameters>
<asp:controlparameter name="pAppId" controlid="txtAppId" propertyname="Text" />
</SelectParameters>
<SelectParameters>
<asp:controlparameter name="pAppId" controlID="txtAppId" propertyname="Text"
Direction="InputOutput" Type="Int32" ConvertEmptyStringToNull="True" />

I tried the following, same error

</SelectParameters>
<asp:SessionParameter
ConvertEmptyStringToNull="True"
DefaultValue="0"
Direction=" InputOutput "
Name="pAppId"
SessionField="app_id"
Size="integer"
Type="String" />
</asp:SqlDataSource>

For some reason the select parameter pAddId is getting set to null and get the following error when the content page is loaded If I hard code the value it works RA-01036: illegal variable name/number Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: Oracle.DataAccess.Client.OracleException: ORA-01036: illegal variable name/number