After installation of the trial Zend version, the main admin page (admin/index.php) is blank. All the other pages are okay. I re-ran the docs/tester.php and it says that my system is okay, and that I have Zend optimizer installed on my system. The other pages under /admin folder are working fine. The user login page opens okay. Only the admin page is blank. I re-downloaded, unzipped, and re-uploaded the admin/index.php, but the problem persists.
Please contact us via helpdesk with ftp info and url. I guess there is some error with upload, but because PHP error_reporting is disabled, you do not see error message.