login control authentication not working with user defined database

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C#

ASP.NET

I am trying to authenticate login control with sql database.But its not working.What am i missing.

Here is my code

private bool Userlogin(string un, string pw)
{
    SqlConnection con = new SqlConnection(constr);
    SqlCommand cmd=new SqlCommand("Select *from UserData where Username= @un and password=@pw",con );
    cmd.Parameters.AddWithValue("@un",un);
    cmd.Parameters.AddWithValue("@pw",pw);
    con.Open();
    string result=Convert.ToString(cmd.ExecuteScalar());
    if (string.IsNullOrEmpty(result)) return false;return true;
}
protected void login1_Authenticate(object sender, AuthenticateEventArgs e)
{
    string un = login1.UserName;
    string pw = login1.Password;
    bool result = Userlogin(un, pw);
    if (result)
    {
        e.Authenticated = true;
        Session["username"] = un;
    }
    else
    {
        e.Authenticated = false;
    }
}