Good day for all community. I have an Joomla 1.5 CMS and when i update JoomSEF plugin - i got no warnings o errors, it's all correct. But now when I trying to manage this module - it's not working all correct, for example when i want to go to configuration - nothing happened, when I try to go to control panel - i see Fatal error: "Call to undefined function json_encode() in /administrator/components/com_sef/view.php on line 31"

Maybe somebody can help me?