[TYPO3-about] Fatal error after upload newsletter extension

[valens rwakageyo]

Hello Every body 
 after upload newsletter extension i get a fatal error and i cant even access to my back end .please somebody help me

Fatal error: Class 'TYPO3\CMS\Core\Utility\ExtensionManagementUtility' not found in /home2/meteolog/public_html/typo3conf/temp_CACHED_FE_psc27e_ext_localconf.php on line 733

this is the website www.meteorwanda.gov.rw


thanks