php SESSION not working with version 2.1

I wrote a plugin called anotherFlickr that uses ajax to load pictures from a flickr account. On the callback page, I use session variables to store information between callbacks. I also put an include to wp-config.php so that I can get wordpress settings. This worked fine up until the recent update to 2.1. Now it seems that I can’t use php session variables any longer. Here’s a quick sample I wrote to demonstrate the problem:


<?
session_start();
require_once( "../../../wp-config.php");
$counter++;
print "You have visited this page $counter times during this session";
session_register("counter");
?>