Call to a member function addData() on a non-object wizardBlock->addData solution: check in app\code\core\Mage\Adminhtml\Block\System\Convert\Gui\Edit if the "Tab" folder or the "upload.php", "view.php", "wizard.php" are missing or corrupted If all the files are there just backup the (edit) folder and replace the files with a fresh copy downloaded from the magento website.