long shot but it could be in the apache config
I had the same issue and I had to create a /etc/httpd/conf/extra/zenphoto.conf file (NOTE this was for arch-linux, where the config files for yr server reside...). This files basically contained
`<Directory /home/httpd/html/MyPhoto>
php_flag display_errors off
AllowOverride all
</Directory>`
Then in /etc/httpd/conf/httpd.conf
in the section where the apache config pulls in specific configs I added:
`Include /etc/httpd/conf/extra/zenphoto.conf`
This works for me, it may/may not work for you