I have a weird problem with Magento 1.7.0.2. After I changed the Apache 2.4 MPM from Prefork to Event, so that it supports HTTP/2.0, I get the below page when I try to open old orders via the Admin back-end whose the Order Comments field contains the symbol "%". If I remove the symbol "%" by manually editing "comment" field at the database table "sales_flat_order_status_history", the problem is resolved.
The weird thing is that the problem does not occur in my test environment of Magento which is the same version and hosted by the same server as my production environment. In addition, I checked the files "/app/code/core/Mage/Adminhtml/Helper/Sales.php" of both my Magento environments with diff command and they are identical.
Warning: vsprintf(): Too few arguments in /app/code/core/Mage/Adminhtml/Helper/Sales.php on line 152
#0 [internal function]: mageCoreErrorHandler(2, 'vsprintf(): Too...', '/home/andrikop/...', 152, Array)
#1 /app/code/core/Mage/Adminhtml/Helper/Sales.php(152): vsprintf('\xCE\xA0\xCE\xA1\xCE\x9F\xCE\xA3\xCE\x9F\xCE\xA7\xCE\x97:...', Array)
#2 /app/code/core/Mage/Adminhtml/Block/Sales/Order/View/Tab/History.php(195): Mage_Adminhtml_Helper_Sales->escapeHtmlWithLinks('\xCE\xA0\xCE\xA1\xCE\x9F\xCE\xA3\xCE\x9F\xCE\xA7\xCE\x97:...', Array)
#3 /app/design/adminhtml/default/default/template/sales/order/view/tab/history.phtml(51): Mage_Adminhtml_Block_Sales_Order_View_Tab_History->getItemComment(Array)
#4 /app/code/core/Mage/Core/Block/Template.php(241): include('/home/andrikop/...')
#5 /app/code/core/Mage/Core/Block/Template.php(272): Mage_Core_Block_Template->fetchView('adminhtml/defau...')
#6 /app/code/core/Mage/Core/Block/Template.php(286): Mage_Core_Block_Template->renderView()
#7 /app/code/core/Mage/Adminhtml/Block/Template.php(81): Mage_Core_Block_Template->_toHtml()
#8 /app/code/core/Mage/Core/Block/Abstract.php(867): Mage_Adminhtml_Block_Template->_toHtml()
#9 /app/code/core/Mage/Adminhtml/Block/Widget/Tabs.php(303): Mage_Core_Block_Abstract->toHtml()
#10 /app/design/adminhtml/default/default/template/widget/tabs.phtml(38): Mage_Adminhtml_Block_Widget_Tabs->getTabContent(Object(Mage_Adminhtml_Block_Sales_Order_View_Tab_History))
#11 /app/code/core/Mage/Core/Block/Template.php(241): include('/home/andrikop/...')
#12 /app/code/core/Mage/Core/Block/Template.php(272): Mage_Core_Block_Template->fetchView('adminhtml/defau...')
#13 /app/code/core/Mage/Core/Block/Template.php(286): Mage_Core_Block_Template->renderView()
#14 /app/code/core/Mage/Adminhtml/Block/Template.php(81): Mage_Core_Block_Template->_toHtml()
#15 /app/code/core/Mage/Core/Block/Abstract.php(867): Mage_Adminhtml_Block_Template->_toHtml()
#16 /app/code/core/Mage/Core/Block/Text/List.php(43): Mage_Core_Block_Abstract->toHtml()
#17 /app/code/core/Mage/Core/Block/Abstract.php(867): Mage_Core_Block_Text_List->_toHtml()
#18 /app/code/core/Mage/Core/Block/Abstract.php(586): Mage_Core_Block_Abstract->toHtml()
#19 /app/code/core/Mage/Core/Block/Abstract.php(530): Mage_Core_Block_Abstract->_getChildHtml('left', true)
#20 /app/design/adminhtml/default/default/template/page.phtml(58): Mage_Core_Block_Abstract->getChildHtml('left')
#21 /app/code/core/Mage/Core/Block/Template.php(241): include('/home/andrikop/...')
#22 /app/code/core/Mage/Core/Block/Template.php(272): Mage_Core_Block_Template->fetchView('adminhtml/defau...')
#23 /app/code/core/Mage/Core/Block/Template.php(286): Mage_Core_Block_Template->renderView()
#24 /app/code/core/Mage/Adminhtml/Block/Template.php(81): Mage_Core_Block_Template->_toHtml()
#25 /app/code/core/Mage/Core/Block/Abstract.php(867): Mage_Adminhtml_Block_Template->_toHtml()
#26 /app/code/core/Mage/Core/Model/Layout.php(555): Mage_Core_Block_Abstract->toHtml()
#27 /app/code/core/Mage/Core/Controller/Varien/Action.php(390): Mage_Core_Model_Layout->getOutput()
#28 /app/code/core/Mage/Adminhtml/controllers/Sales/OrderController.php(119): Mage_Core_Controller_Varien_Action->renderLayout()
#29 /app/code/core/Mage/Core/Controller/Varien/Action.php(419): Mage_Adminhtml_Sales_OrderController->viewAction()
#30 /app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('view')
#31 /app/code/core/Mage/Core/Controller/Varien/Front.php(176): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#32 /app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch()
#33 /app/Mage.php(683): Mage_Core_Model_App->run(Array)
#34 /index.php(106): Mage::run('base', 'website')
#35 {main}
