Mage registry key "_singleton/iamgento_megamenu/observer" already exists

#0 /domains/networldsports.co.uk/http/app/Mage.php(223): Mage::throwException('Mage registry k...')
#1 /domains/networldsports.co.uk/http/app/Mage.php(477): Mage::register('_singleton/iamg...', false)
#2 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/App.php(1336): Mage::getSingleton('iamgento_megame...')
#3 /domains/networldsports.co.uk/http/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('core_block_abst...', Array)
#4 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Block/Abstract.php(910): Mage::dispatchEvent('core_block_abst...', Array)
#5 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/Layout.php(555): Mage_Core_Block_Abstract->toHtml()
#6 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Action.php(390): Mage_Core_Model_Layout->getOutput()
#7 /domains/networldsports.co.uk/http/app/code/core/Mage/Cms/Helper/Page.php(137): Mage_Core_Controller_Varien_Action->renderLayout()
#8 /domains/networldsports.co.uk/http/app/code/core/Mage/Cms/Helper/Page.php(52): Mage_Cms_Helper_Page->_renderPage(Object(Mage_Cms_IndexController), 'no-route')
#9 /domains/networldsports.co.uk/http/app/code/core/Mage/Cms/controllers/IndexController.php(75): Mage_Cms_Helper_Page->renderPage(Object(Mage_Cms_IndexController), 'no-route')
#10 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Cms_IndexController->noRouteAction()
#11 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('noRoute')
#12 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#13 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#14 /domains/networldsports.co.uk/http/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#15 /domains/networldsports.co.uk/http/index.php(92): Mage::run('nws_uk', 'website')
#16 {main}