Crystal Reports :: Asking For Parameter After First Page Display

I am trying to populate a report with parameters from session. Problem I am getting is that it is asking for parameter after I click the 2nd page of report. If I remove the Session.Remove it works good. Is there anyway to clear session after the first time the code executes? Here is my report viewer page code

public partial class setups_ftreaty_ft_mstmt : System.Web.UI.Page
{
ReportDocument rptDoc = null;
protected void Page_Init(object sender, EventArgs e)
{
string reportName = Request.QueryString["reportName"].ToString();
rptDoc = new ReportDocument();
rptDoc = ReportFactory.GetReport(rptDoc.GetType());
string path = Server.MapPath("~/reports/ptreaty/" + reportName + ".rpt");
rptDoc.Load(path);
if (Session["ptRepParams"] != null)
{
Hashtable repParams = (Hashtable)Session["ptRepParams"];
foreach (string param in repParams.Keys)
{
rptDoc.SetParameterValue(param, repParams[param].ToString());
}
}..............