I have tried removing the english language, but that still doesnt fix the problems with filtering.

As the person above me i have the error:
Code:
[05-Jun-2014 12:15:58 Europe/Amsterdam] PHP Warning:  trim() expects parameter 1 to be string, array given in /var/www/vhosts/domain/httpdocs/shop/includes/functions/functions_general.php on line 63
[05-Jun-2014 12:15:58 Europe/Amsterdam] PHP Warning:  trim() expects parameter 1 to be string, array given in /var/www/vhosts/domain/httpdocs/shop/includes/functions/functions_general.php on line 63

Here you can see how buggy it is:
http://www.etcoevorden.nl/shop/index...ex&cPath=23_42

This shows a lot of products, but when clicking on the "Discovery 1 1990-1998" Filter on the left side

It doesnt show me any results (in the bottom it shows -> Artikel 1 tot 10 (van 18 artikelen) (so it should have at least 1 result)

If you check one of the products in this category -> http://www.etcoevorden.nl/shop/index...&products_id=8

It does show Attribute -> "Discovery 1 1990-1998" in the bottom so it should be able to find it ?

Im currently running Zencart 1.5.1 and i have tried to add the fixes posted by dr blyte