Magento Admin Config settings won't save - php

Question

I have a Magento 1.8 installation which was working fine up until yesterday evening at which point changing any config settings in the admin area stopped working.
E.g. If I change 'store name' to anything different and clicking save: it says "The configuration has been saved" in the green bar at the top but the value stays as it previously was.
Checking in phpMyAdmin the value is unchanged, however you can change it manually in phpMyAdmin and this will be reflected in the admin backend.
Switching on developer mode, initially got me the following when I tried to load any page:
Strict Notice: Only variables should be passed by reference in /home/user/dev/lib/Varien/Db/Adapter/Pdo/Mysql.php on line 2765
#0 /home/user/dev/lib/Varien/Db/Adapter/Pdo/Mysql.php(2765): mageCoreErrorHandler(2048, 'Only variables ...', '/home/user/de...', 2765, Array)
#1 /home/user/dev/lib/Varien/Data/Collection/Db.php(483): Varien_Db_Adapter_Pdo_Mysql->prepareSqlCondition('path', Array)
#2 /home/user/dev/lib/Varien/Data/Collection/Db.php(414): Varien_Data_Collection_Db->_getConditionSql('path', Array)
#3 /home/user/dev/lib/Varien/Data/Collection/Db.php(385): Varien_Data_Collection_Db->_translateCondition('path', Array)
#4 /home/user/dev/app/code/core/Mage/Core/Model/Resource/Config/Data/Collection.php(58): Varien_Data_Collection_Db->addFieldToFilter('path', Array)
#5 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config/Data.php(306): Mage_Core_Model_Resource_Config_Data_Collection->addScopeFilter('default', 0, 'general')
#6 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config/Data.php(292): Mage_Adminhtml_Model_Config_Data->_getPathConfig('general', false)
#7 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config/Data.php(221): Mage_Adminhtml_Model_Config_Data->_getConfig(false)
#8 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config/Data.php(334): Mage_Adminhtml_Model_Config_Data->load()
#9 /home/user/dev/app/code/core/Mage/Paypal/Model/Observer.php(134): Mage_Adminhtml_Model_Config_Data->getConfigDataValue('paypal/general/...')
#10 /home/user/dev/app/code/core/Mage/Core/Model/App.php(1338): Mage_Paypal_Model_Observer->loadCountryDependentSolutionsConfig(Object(Varien_Event_Observer))
#11 /home/user/dev/app/code/core/Mage/Core/Model/App.php(1317): Mage_Core_Model_App->_callObserverMethod(Object(Mage_Paypal_Model_Observer), 'loadCountryDepe...', Object(Varien_Event_Observer))
#12 /home/user/dev/app/Mage.php(447): Mage_Core_Model_App->dispatchEvent('adminhtml_init_...', Array)
#13 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config.php(93): Mage::dispatchEvent('adminhtml_init_...', Array)
#14 /home/user/dev/app/code/core/Mage/Adminhtml/Model/Config.php(63): Mage_Adminhtml_Model_Config->_initSectionsAndTabs()
#15 /home/user/dev/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(88): Mage_Adminhtml_Model_Config->getSections('general')
#16 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#17 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(250): Mage_Core_Controller_Varien_Action->dispatch('edit')
#18 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#19 /home/user/dev/app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch()
#20 /home/user/dev/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#21 /home/user/dev/index.php(87): Mage::run('', 'store')
#22 {main}
Looking up /home/user/dev/lib/Varien/Db/Adapter/Pdo/Mysql.php on line 2765:
$key = key(array_intersect_key($condition, $conditionKeyMap));
Which made no sense to me, but something to do with MySQL seemed like I might be on the right track... I googled the error and found this: http://www.magentocommerce.com/boards/v/viewthread/266575/ - and tried the suggestion of replacing line 2795 with:
$tmp = array_intersect_key($condition, $conditionKeyMap);
$key = key($tmp);
Which resulted in the following dev mode error:
Method "addJqueryLibrary" is not defined in "Magentothem_Upsellslider_Model_Layout_Generate_Observer"
#0 /home/user/dev/app/code/core/Mage/Core/Model/App.php(1340): Mage::throwException('Method "addJque...')
#1 /home/user/dev/app/code/core/Mage/Core/Model/App.php(1317): Mage_Core_Model_App->_callObserverMethod(Object(Magentothem_Upsellslider_Model_Layout_Generate_Observer), 'addJqueryLibrar...', Object(Varien_Event_Observer))
#2 /home/user/dev/app/Mage.php(447): Mage_Core_Model_App->dispatchEvent('controller_acti...', Array)
#3 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Action.php(351): Mage::dispatchEvent('controller_acti...', Array)
#4 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Action.php(269): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
#5 /home/user/dev/app/code/core/Mage/Adminhtml/Controller/Action.php(275): Mage_Core_Controller_Varien_Action->loadLayout(NULL, true, true)
#6 /home/user/dev/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(95): Mage_Adminhtml_Controller_Action->loadLayout()
#7 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_System_ConfigController->editAction()
#8 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(250): Mage_Core_Controller_Varien_Action->dispatch('edit')
#9 /home/user/dev/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#10 /home/user/dev/app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch()
#11 /home/user/dev/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#12 /home/user/dev/index.php(87): Mage::run('', 'store')
#13 {main}
If you switch developer mode off now, the same thing happens, says its saved but no change.
Just found in /var/exception.log another error that says:
exception 'Mage_Core_Exception' with message 'Invalid block type: Fishpig_FPAdmin_Block_Adminhtml_Extend' in /home/pieboy/dev/app/Mage.php:594
(followed by another stack trace)
I'm pretty much at my wits end with what to try next and out of my depth. The store is using a paid for theme which included a lot of extensions which I didn't personally install, but it has been working completely fine up until now.
The most recent extension I installed was this:
http://www.magentocommerce.com/magento-connect/stripe-for-magento.html
As far as I could tell it all went smoothly, and I've been editing config settings since, but it was when I went to enable it in the payment methods area that I noticed the problem.
I know this was a lot of reading, but was just trying to get down all the info. Any suggestions at all on how to debug from here are welcome.
EDIT: I uninstalled Fishpig and Magentothem upsellslider extensions, and now I get no errors or exceptions at all in dev mode but still the same behaviour with config settings not saving.

Answer 1

With the help of my hosting company, we tracked this down to being caused by suhosin, they increased the following suhosin limits in the php.ini file for my server which resolved the issue:
suhosin.post.max_vars = 1000
suhosin.request.max_vars = 1000
(Thought I would update here in case anyone in the same boat googles it!)