Mediawiki debug after upgrade

Mediawiki has been installed on a private server. Upon moving to another server, mediawiki wont load with the following error: Fatal error: Call to undefined method XML::encodeJsVar() in /root/science30/coaspedia/includes/[login to view URL] on line 345 Call Stack: 0.0003 365272 1. {main}() /root/science30/coaspedia/[login to view URL] 1.0669 63714396 2. MediaWiki->finalCleanup() /root/science30/coaspedia/[login to view URL] 1.1349 63714392 3. OutputPage->output() /root/science30/coaspedia/includes/[login to view URL] 1.1354 63756368 4. SkinTemplate->outputPage() /root/science30/coaspedia/includes/[login to view URL] 1.2418 63959980 5. OutputPage->headElement() /root/science30/coaspedia/includes/[login to view URL] 1.2469 63972184 6. OutputPage->getHeadScripts() /root/science30/coaspedia/includes/[login to view URL] 1.2469 63972264 7. Skin::makeGlobalVariablesScript() /root/science30/coaspedia/includes/[login to view URL] 1.2512 63985388 8. Skin::makeVariablesScript() /root/science30/coaspedia/includes/[login to view URL] This needs debugging. That is the job.