Method "coreBlockAbstractToHtmlBefore" is not defined in ""

#0 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/App.php(1360): Mage::throwException('Method "coreBlo...')
#1 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/App.php(1337): Mage_Core_Model_App->_callObserverMethod(false, 'coreBlockAbstra...', Object(Varien_Event_Observer))
#2 /domains/networldsports.co.uk/http/app/Mage.php(448): Mage_Core_Model_App->dispatchEvent('core_block_abst...', Array)
#3 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Block/Abstract.php(910): Mage::dispatchEvent('core_block_abst...', Array)
#4 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/Layout.php(555): Mage_Core_Block_Abstract->toHtml()
#5 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Action.php(390): Mage_Core_Model_Layout->getOutput()
#6 /domains/networldsports.co.uk/http/app/code/core/Mage/Catalog/controllers/CategoryController.php(161): Mage_Core_Controller_Varien_Action->renderLayout()
#7 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Catalog_CategoryController->viewAction()
#8 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('view')
#9 /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))
#10 /domains/networldsports.co.uk/http/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#11 /domains/networldsports.co.uk/http/app/Mage.php(683): Mage_Core_Model_App->run(Array)
#12 /domains/networldsports.co.uk/http/index.php(92): Mage::run('nws_uk', 'website')
#13 {main}