All is in the title

/////// My installation ///////
Wordpress 2.2 + PhpWebGallery 1.7
I install :
- Photon plugin in WP and I import all users from PWG in WP
- modify config_local.inc in PWG
==>Now There is only one single table to store the users (wp_user) and the authentification works very well in WP. And the user need to authenticate again in PWG (same user and same login) and it’s work well.
But there is no single sign on (from WP to PWG)… what I expect for my users !

/////// My problem ///////
When user log in with WP wp-login.php web page, 4 cookies are generated : 2 for WP and 2 for PWG (the script is in photon.php file)
But the Cookies for PWG don’t work to authenticate the user in PWG. As a consequence, the user need to enter again his credential in PWG.

Have you experience the same issue or is it the normal behavior?
Regards