Add filter problems

[cumbe]

Thanks mvlcek;

I have checked alls plugins, and have 2 plugins that use add_filter: simple image gallery, and dominion jcart.
In both it is the same, writes the code that calls to function, but not works; by example, if in a page i write: (% dcart :toets %), in web appears (% dcart :toets %) and must appears the list of products...

Normally, it is fixed calling to function directly with <?php....., but i want to see where is the problem for that add_filter works good.

Regards.

PD: i´m sorry for my english.