TYPO3 Core

i tried both introduction package and dummy 6.0beta1

when launching the (new) extension manager i get lots of "???????????????????????????????" and then Uncaught TYPO3 Exception

Class TYPO3\CMS\Extensionmanager\Utility\DatabaseUtility does not exist 

ReflectionException thrown in file
/Sites/typo3_src-6.0.0beta1/typo3/sysext/extbase/Classes/Object/Container/ClassInfoFactory.php in line 99.

the full log in Log module is:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: Class TYPO3\CMS\Extensionmanager\Utility\DatabaseUtility does not exist | ReflectionException thrown in file /Sites/typo3_src-6.0.0beta1/typo3/sysext/extbase/Classes/Object/Container/ClassInfoFactory.php in line 99. Requested URL: http://localhost/dummy-6.0.0beta1/typo3/mod.php?M=tools_ExtensionmanagerExtensionmanager

i'm under OSX 10.8, PHP 5.3.13
the system works perfectly with any TYPO3 version with lots of extBase development i do...

i tried importing static data, reimporting db structures, clearing caches, there's no PHP accelerator
nothing!