Hi
I just signed up to let you know that OC version 1.5.6 gave this error months ago:

1. ... product_total  ...

2. Notice: Undefined variable: filter_name in /home/MYWEBSITE/vqmod/vqcache/vq2-catalog_controller_product_search.php on line 465

3. Notice: Undefined variable: filter_category_id in /home/MYWEBSITE/vqmod/vqcache/vq2-catalog_controller_product_search.php on line 465

 But I had the 'initial' 0.4 Piwik extension installed on [did not notice!] and as soon as I replaced it with version 1.0, it solved the problem on OC 1.5.6.

I now have OC 1.5.6.1 and it has come back, but only with:

filter_name
filter_category_id

Just to inform you, I am no coder and I do not wish to bother you guys more, although I have been playing with PHP for a while, I have no basics [yet]!

So, I hope you are going to fix it soon

;p]