/**
 * Implementation of hook_perm().
 */
function odp_perm() {
  return array('log in');
}

/**
 * Implementation of hook_user
 * lock out without the 'log in' permission
 */
function odp_user($op, &$edit, &$account, $category = NULL) {
    if ($op == 'login' && ! user_access('log in')) {
      drupal_set_message("You do not have access to log in.", "error");
      drupal_goto('logout'); //doesn't work
      drupal_goto('content/party-tonight'); //also doesn't work
    }
}

/**
 * Implementation of hook_user
 * lock out without the 'log in' permission
 */
function odp_user($op, &$edit, &$account, $category = NULL) {
    if ($op == 'login' && ! user_access('log in')) {
        global $user;
        $user = drupal_anonymous_user();
        drupal_set_message("You don't have permission to log in");

    }
}

/**
 * Implementation of hook_user
 * lock out without the 'log in' permission
 */
function odp_user($op, &$edit, &$account, $category = NULL) {
    if ($op == 'login' && ! user_access('log in')) {
        drupal_set_message("You don't have permission to log in");

        //prevent login
        header("Location: http://www.example.com/?q=logout");
        // header("Location: http://www.example.com/logout"); if using clean URLs
    }
}