[TYPO3-english] Error - Call to undefined method

[Jacob Roe]

I have just installed typo3 6.2.19 by the use of symlinks.

On the backend I get this:
Oops, an error occurred!
Call to undefined method TYPO3\CMS\Form\Utility\FormUtility::getInstance()

On the frontend I get this:
Fatal error: Uncaught TypeError: Argument 1 passed to TYPO3\CMS\Core\Error\AbstractExceptionHandler::handleException() must be an instance of Exception, instance of Error given in /var/typo3_src/typo3_src-6.2.19/typo3/sysext/core/Classes/Error/AbstractExceptionHandler.php:38 Stack trace: #0 [internal function]: TYPO3\CMS\Core\Error\AbstractExceptionHandler->handleException(Object(Error)) #1 {main} thrown in /var/typo3_src/typo3_src-6.2.19/typo3/sysext/core/Classes/Error/AbstractExceptionHandler.php on line 38