State Management :: Pass Value To The Next Page?

I would like to pass vaule to the next aspx page. I am using sesseion variable, but I still get the error.

protected void sUBMIT_Click(object sender, EventArgs e)
{
Session["PID"] = DdlPID.SelectedValue;
Session["GID"] = DdlGID.SelectedValue;
PID = (string)Session["PID"];
GID = (string)Session["GID"];
Server.Transfer("Submit.aspx");
}

Next submit page

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
LblPID.Text = PID;
LblGID.Text = GID;
}

ERROR: the name 'PID' does not exist in the current context.