Active Directory login works for the second time only

Question

I implemented an authentication via AD in my application. It only works on the second try, it does not work on the first.

How do I resolve?

DirectoryEntry directoryEntry = new DirectoryEntry(path, domUser, password, AuthenticationTypes.Secure);

//Pesquisa na directoria
DirectorySearcher directorySearcher = new DirectorySearcher(directoryEntry);

try
{   
    //Procura credenciais e autentica utilizador
    SearchResult searchResult = directorySearcher.FindOne();

    //Procura utilizador por username e armazena em sessão o seu nome completo
    using(var ctx = new PrincipalContext(ContextType.Domain))
    {
        using (UserPrincipal user = UserPrincipal.FindByIdentity(ctx, username))
        {
            if (user != null)
            {
                string name = user.DisplayName;

                //Armazena nome completo do utilizador
                Session["name"] = name;
            }
        }
    }

    Session["LoggedIn"] = true;

    directorySearcher.Dispose();

    Response.Redirect("~/Home/Index");
}
catch
{
    Response.Redirect("~/Home/Login");
}

PS: I deleted domain information from the code for privacy reasons of my employer