Error: Mage registry key "_singleton/rkt_jscssforsb/observer" already exists

Question

I am building a magento B2B webshop and now I cant do anything with it because of some error

a:5:{i:0;s:69:"Mage registry key "_singleton/rkt_jscssforsb/observer" already exists";i:1;s:3637:"#0 app/Mage.php(223): Mage::throwException('Mage registry k...')
#1 app/Mage.php(477): Mage::register('_singleton/rkt_...', false)
#2 app/code/core/Mage/Core/Model/App.php(1316): Mage::getSingleton('rkt_jscssforsb/...')
#3 app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('adminhtml_block...', Array)
#4 app/code/core/Mage/Adminhtml/Block/Template.php(80): Mage::dispatchEvent('adminhtml_block...', Array)
#5 app/code/core/Mage/Core/Block/Abstract.php(919): Mage_Adminhtml_Block_Template->_toHtml()
#6 app/code/core/Mage/Adminhtml/Block/Dashboard/Diagrams.php(55): Mage_Core_Block_Abstract->toHtml()
#7 app/code/core/Mage/Core/Block/Abstract.php(293): Mage_Adminhtml_Block_Dashboard_Diagrams->_prepareLayout()
#8 app/code/core/Mage/Core/Model/Layout.php(456): Mage_Core_Block_Abstract->setLayout(Object(Mage_Core_Model_Layout))
#9 app/code/core/Mage/Adminhtml/Block/Dashboard.php(66): Mage_Core_Model_Layout->createBlock('adminhtml/dashb...')
#10 app/code/core/Mage/Core/Block/Abstract.php(293): Mage_Adminhtml_Block_Dashboard->_prepareLayout()
#11 app/code/core/Mage/Core/Model/Layout.php(456): Mage_Core_Block_Abstract->setLayout(Object(Mage_Core_Model_Layout))
#12 app/code/core/Mage/Core/Model/Layout.php(472): Mage_Core_Model_Layout->createBlock('adminhtml/dashb...', 'dashboard')
#13 app/code/core/Mage/Core/Model/Layout.php(239): Mage_Core_Model_Layout->addBlock('adminhtml/dashb...', 'dashboard')
#14 app/code/core/Mage/Core/Model/Layout.php(205): Mage_Core_Model_Layout->_generateBlock(Object(Mage_Core_Model_Layout_Element), Object(Mage_Core_Model_Layout_Element))
#15 app/code/core/Mage/Core/Model/Layout.php(210): Mage_Core_Model_Layout->generateBlocks(Object(Mage_Core_Model_Layout_Element))
#16 app/code/core/Mage/Core/Controller/Varien/Action.php(344): Mage_Core_Model_Layout->generateBlocks()
#17 app/code/core/Mage/Core/Controller/Varien/Action.php(269): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
#18 app/code/core/Mage/Adminhtml/Controller/Action.php(275): Mage_Core_Controller_Varien_Action->loadLayout(NULL, true, true)
#19 app/code/core/Mage/Adminhtml/controllers/DashboardController.php(40): Mage_Adminhtml_Controller_Action->loadLayout()
#20 app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_DashboardController->indexAction()
#21 app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(250): Mage_Core_Controller_Varien_Action->dispatch('index')
#22 app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#23 app/code/core/Mage/Core/Model/App.php(354): Mage_Core_Controller_Varien_Front->dispatch()
#24 app/Mage.php(684): Mage_Core_Model_App->run(Array)
#25 index.php(87): Mage::run('', 'store')
#26 {main}";s:3:"url";s:81:"/Magento/index.php/ma_admin/dashboard/index/key/f1e58b7d15977224c929ac0010422f85/";s:11:"script_name";s:18:"/Magento/index.php";s:4:"skin";s:5:"admin";}

Answer 1

Your PHP developer should be able to solve the exact problem with this trace, but to explain the Problem:

You have an observer which calls rkt_jscssforsb/observer as singleton (the default) but this model could not be loaded, so it saves false in the registry, which is not recognized by the next call of this singleton as it has the value false, so it is tried again to call this singleton, but the registry does not allow to write a value, which already exist.

Thats why you get the error message:
Mage registry key "_singleton/rkt_jscssforsb/observer" already exists

As you noted in your comment, you uninstalled a module, if this module had the name rkt_jscssforsb you should first try to clean the cache, maybe forcefully by delete magento/var/cache/* or try to grep/search trough the code for the occurence of it to clean up the rest

Answer 2

I faced the same issue while removing the extension manually.

Approach to follow:

1. Revert the changes made.
2. With that, you will get the admin panel. Now, disable compliation at system>tools>compilation & disable all the cache types under at system>cache management.
3. Now remove the extension the way you were removing.
4. Go to admin panel, it must be working now.
   Clear cache from system>cache management.

Hope, this help to someone!

Answer 3

Check if your event observer xml code in your module's config.xml is all correct.

It should be something like this:

<events>
    <event_name_that_you_are_working_on>
        <observers>
            <some_unique_identifier>
                <type>singleton</type>
                <class>YourNamespace_YourModule_Model_Observer</class>
                <method>functionNameInYourObserver</method>
            </some_unique_identifier>
        </observers>
    </event_name_that_you_are_working_on>
</events>

I once got this kind of error because I was using modulename/observer inside class node. Using full class name (YourNamespace_YourModule_Model_Observer) solved the error for me.

In your module's event-observer xml code, you might be using class like below:

<class>yourmodule/observer</class>

Try using this instead (as done in above event-observer xml code):

<class>YourNamespace_YourModule_Model_Observer</class>