Ok.
First I must say a big thank you for your support, Stephen.
Now, I've just uploaded the last Zenphoto trunk (trunk-r3436) and I get :
Strict Standards: date_default_timezone_get() [function.date-default-timezone-get]: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/Chicago' for 'CST/-6.0/no DST' instead in /home/mysuperwebsite/public_html/zp-core/functions-basic.php on line 23
Warning: Cannot modify header information - headers already sent by (output started at /home/mysuperwebsite/public_html/zp-core/functions-basic.php:23) in /home/mysuperwebsite/public_html/zp-core/admin.php on line 14
Do you have any idea about it ?