Negeneruje mi feed pre Heureku

Pouzivam Woocommerce 3.1.1 a nepodarilo sa mi este vygenerovat feed pre heureku. Hlasi mi hlasku:
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<b>Fatal error</b>: Class ‘XMLWriter’ not found in <b>/www/b/e/u95274/public_html/wp-content/plugins/ceske-sluzby-master/includes/class-ceske-sluzby-xml.php</b> on line <b>712</b><br />

Mam nainstalovany modul 0.6-alpha.
Viete mi poradit kde by mohol byt problem? Vopred velmi dakujem.

The page I need help with: [log in to see the link]