Thread:Extension talk:CategoryTree/Fatal error CategoryTreePage.php

I just upgraded to mediawiki 1.19.9. The CategoryTree extension for 1.19 gives the following error Fatal error: Call to undefined method SpecialPage::specialpage CategoryTreePage.php on line 27

Any idea how to fix this one? Does it work with 1.19.9 or should I have to downgrade? If so, which version of mediawiki does it perfectly work with?