Not sure where to write, but just want to inform regarding what I think is a magento bug. It appears if you use magento 1.9.3.1 and php 5.6. It does not appear if you use php 5.5.
To reproduce the exception you have to do this:
1. Install magento 1.9.3.1
2. log in and Reindex
3. Activate logs in magento admin -> system -> configuration -> advanced -> developer -> Log settings
4. Flush cache
5. log out and log in.
6. go to System -> Configuration -> General -> Design and change from rwd to default in the field "Current Package Name". Click save. (I have done this test exactly as the steps I write so i don't have anything else installed but if you have any other theme installed then you can just activate that theme instead of default as I have. I have tried it myself and I still get the exception errors.)
7. Switch to another website or store view in the drop down where it says "Current Configuration Scope:"
8. When step 7 is completed then you will find exception.log in /var/log
This is what happens in exception.log:
2016-11-20T20:21:38+00:00 ERR (3):
exception 'Exception' with message 'Error during unserialization' in html/lib/Unserialize/Parser.php:60
Stack trace:
#0 html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize(Object(Mage_Core_Model_Config_Element))
#1 html/app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php(37): Mage_Core_Helper_UnserializeArray->unserialize(Object(Mage_Core_Model_Config_Element))
#2 html/app/code/core/Mage/Core/Model/Config/Data.php(78): Mage_Adminhtml_Model_System_Config_Backend_Serialized->_afterLoad()
#3 html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(334): Mage_Core_Model_Config_Data->afterLoad()
#4 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))
#5 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))
#6 html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#7 html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#8 html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#9 html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#10 html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 html/index.php(83): Mage::run('default', 'store')
#14 {main}
2016-11-20T20:21:38+00:00 ERR (3):
exception 'Exception' with message 'Error during unserialization' in html/lib/Unserialize/Parser.php:60
Stack trace:
#0 html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize(Object(Mage_Core_Model_Config_Element))
#1 html/app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php(37): Mage_Core_Helper_UnserializeArray->unserialize(Object(Mage_Core_Model_Config_Element))
#2 html/app/code/core/Mage/Core/Model/Config/Data.php(78): Mage_Adminhtml_Model_System_Config_Backend_Serialized->_afterLoad()
#3 html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(334): Mage_Core_Model_Config_Data->afterLoad()
#4 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))
#5 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))
#6 html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#7 html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#8 html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#9 html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#10 html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 html/index.php(83): Mage::run('default', 'store')
#14 {main}
2016-11-20T20:21:38+00:00 ERR (3):
exception 'Exception' with message 'Error during unserialization' in html/lib/Unserialize/Parser.php:60
Stack trace:
#0 html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize(Object(Mage_Core_Model_Config_Element))
#1 html/app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php(37): Mage_Core_Helper_UnserializeArray->unserialize(Object(Mage_Core_Model_Config_Element))
#2 html/app/code/core/Mage/Core/Model/Config/Data.php(78): Mage_Adminhtml_Model_System_Config_Backend_Serialized->_afterLoad()
#3 html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(334): Mage_Core_Model_Config_Data->afterLoad()
#4 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))
#5 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))
#6 html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#7 html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#8 html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#9 html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#10 html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 html/index.php(83): Mage::run('default', 'store')
#14 {main}
2016-11-20T20:21:38+00:00 ERR (3):
exception 'Exception' with message 'Error during unserialization' in html/lib/Unserialize/Parser.php:60
Stack trace:
#0 html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize(Object(Mage_Core_Model_Config_Element))
#1 html/app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php(37): Mage_Core_Helper_UnserializeArray->unserialize(Object(Mage_Core_Model_Config_Element))
#2 html/app/code/core/Mage/Core/Model/Config/Data.php(78): Mage_Adminhtml_Model_System_Config_Backend_Serialized->_afterLoad()
#3 html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(334): Mage_Core_Model_Config_Data->afterLoad()
#4 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))
#5 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))
#6 html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#7 html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#8 html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#9 html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#10 html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 html/index.php(83): Mage::run('default', 'store')
#14 {main}
2016-11-20T20:21:38+00:00 ERR (3):
exception 'Exception' with message 'Error during unserialization' in html/lib/Unserialize/Parser.php:60
Stack trace:
#0 html/app/code/core/Mage/Core/Helper/UnserializeArray.php(44): Unserialize_Parser->unserialize(Object(Mage_Core_Model_Config_Element))
#1 html/app/code/core/Mage/Adminhtml/Model/System/Config/Backend/Serialized.php(37): Mage_Core_Helper_UnserializeArray->unserialize(Object(Mage_Core_Model_Config_Element))
#2 html/app/code/core/Mage/Core/Model/Config/Data.php(78): Mage_Adminhtml_Model_System_Config_Backend_Serialized->_afterLoad()
#3 html/app/code/core/Mage/Adminhtml/Block/System/Config/Form.php(334): Mage_Core_Model_Config_Data->afterLoad()
#4 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))
#5 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))
#6 html/app/code/core/Mage/Adminhtml/Block/System/Config/Edit.php(92): Mage_Adminhtml_Block_System_Config_Form->initForm()
#7 html/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(107): Mage_Adminhtml_Block_System_Config_Edit->initForm()
#8 html/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#9 html/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('edit')
#10 html/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 html/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 html/index.php(83): Mage::run('default', 'store')
#14 {main}
