[TYPO3-english] Migration 4.5 to 6.2 Bootstrap not found

[TSniper]

Hello,

After migration to typo3 6.2 from typo3 4.5 i have this error :
Bootstrap' not found : 
( ! ) Fatal error: Class 'TYPO3\CMS\Core\Core\Bootstrap' not found in C:\wamp\www\project\typo3\sysext\cms\tslib\index_ts.php on line 32

[11-Mar-2015 14:16:30 Europe/Paris] PHP Stack trace:

[11-Mar-2015 14:16:30 Europe/Paris] PHP   1. {main}() C:\wamp\www\project\index.php:0

[11-Mar-2015 14:16:30 Europe/Paris] PHP   2. require() C:\wamp\www\tdt\project.php:83

thanks in advance for any help