Magento 1.9 – Error in Configuration Scope ‘Default Config’ in General>Web

When going to Default Config > Web I get the following error.

There has been an error processing your request

Invalid config field backend model: adminhtml/system_config_backend_web_secure_offloaderheader
Trace:
#0 /home/wengkomole/public_html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(328): Mage::throwException('Invalid config ...')
#1 /home/wengkomole/public_html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(229): Mage_Adminhtml_Block_System_Config_Form->initFields(Object(Varien_Data_Form_Element_Fieldset), Object(Mage_Core_Model_Config_Element), Object(Mage_Core_Model_Config_Element))
#2 /home/wengkomole/public_html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(164): Mage_Adminhtml_Block_System_Config_Form->_initGroup(Object(Varien_Data_Form), Object(Mage_Core_Model_Config_Element), Object(Mage_Core_Model_Config_Element))
#3 /home/wengkomole/public_html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#4 /home/wengkomole/public_html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#5 /home/wengkomole/public_html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#6 /home/wengkomole/public_html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#7 /home/wengkomole/public_html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#8 /home/wengkomole/public_html/app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch()
#9 /home/wengkomole/public_html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#10 /home/wengkomole/public_html/index.php(87): Mage::run('', 'store')
#11 {main}

On the other hand when selecting current configuration scope (Main Website) I don't get the error.