Notice: Use of undefined constant filter - assumed 'filter' in preg_replace() (.../modules/drutex/drutex.module(363) : regexp code).

Dear All,
I try to use DruTex for the first time here : http://reza.rumahilmu.me - It is able to render my TeX code, but I still got error on my frontpage that is looked like this :

Notice: Use of undefined constant filter - assumed 'filter' in preg_replace() (line 1 of /home/rezaerv/public_html/modules/drutex/drutex.module(363) : regexp code).
Notice: Trying to get property of non-object in drutex_linebreak_node2html_postprocess() (line 49 of /home/rezaerv/public_html/modules/drutex/drutex_linebreak.inc).

What should I do ?

Thank You,

Regards,
Reza Ervani
Rumah Ilmu Indonesia Foundation
www.rumahilmu.or.id