Installing WP through a custom installer via iFrame

Hi,
im trying to install WP through a custom file, via an iFrame in the parent directory.

my website at http://www.domain.com
WP files in http://www.domain.com/demo/

-> http://www.domain.com/install.php my installer.
|–> has an iFrame => http://www.domain.com/demo/wp-custom-install.php

it gets installed alright, but when i log in thru admin, via the pwd so provided, i am getting an error:

You do not have sufficient permissions to access this page.

the following is the cut down version of the code im using:
[stripped out all validations]

<?php
	define('WP_DEBUG', true);
	define('WP_INSTALLING', true);

	require_once('./wp-blog-header.php'); 

	if( !isset($_GET['wp_pbb_call']) || $_GET['wp_pbb_call']!='create-blog') wp_die(".");

	$DATA = '';
	$tt = '';

	require_once('./wp-admin/includes/upgrade.php');

	$result = wp_install($_GET['blog_title'], 'admin', $_GET['blog_email'], $_GET['blog_public']);
	extract($result, EXTR_SKIP);
// html follows //