Fatal error: Class 'Manifest' not found

During the install of Piwik 1.6 on page 2. System Check I get the following error:
Fatal error: Class ‘Manifest’ not found in …/core/Piwik.php on line 612

Any suggestions what could be causing the error?

Server Details: Apache 2.0 and PHP 5.2

Please reupload all piwik files, some are missing?

Thank you Matt, I reuploaded all files and that fixed the problem.