Admiror Gallery cannot create thumbnails in /var/www/www.energyvalley.nl/www2/plugins/content/AdmirorGallery/thumbs/Oldenburger_30_november_dec/
Check folder permmisions!
Admiror Gallery: 3.0
Server OS:Apache/2.2.22 (Ubuntu)
Client OS:Unknown
PHP:5.3.10-1ubuntu3.1