I'm new to Magento and installed today the SUPEE7405 patch without SSH.
Now I have a blank admin page and cant get it back running. I cleared var/session and var/cache. I checked the includes/config.php that the compiler is disabled. I activated the error message and received
Fatal error: Class 'Mage_Core_Helper_UnserializeArray' not found in app/Mage.php on line 547