Admiror Gallery cannot create thumbnails in /var/www/clients/client1/web1/web/plugins/content/AdmirorGallery/thumbs/2012_szkola_letnia/
Check folder permmisions!
Admiror Gallery: 3.0
Server OS:Apache/2.2.22 (Debian)
Client OS:Unknown
PHP:5.4.35-0+deb7u2