I just installed a new theme and after clearing hte cache when i tried to login to the admin,it is showing blank page. Further debugging lead to the following:
exception 'Mage_Core_Exception' with message 'Invalid block type:W3Themes_Themeoptions_Block_Adminhtml_Page_Menu' in /var/www/demo.xyz.com/app/Mage.php:563
Stack trace: > #0 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(469): Mage::throwException('Invalid block t...')
#1 /var/www/demo.xyz.com/app/code/local/Aitoc/Aitsys/Model/Core/Layout.php(10): Mage_Core_Model_Layout->getBlockInstance('adminhtml/page...', Array)
#2 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(411): Aitoc_Aitsys_Model_Core_Layout->getBlockInstance('adminhtml/page...', Array)
#3 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(446): Mage_Core_Model_Layout->createBlock('adminhtml/page_...', 'menu')
#4 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(238): Mage_Core_Model_Layout->addBlock('adminhtml/page_...', 'menu')
#5 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(204): Mage_Core_Model_Layout->_generateBlock(Object(Mage_Core_Model_Layout_Element), Object(Mage_Core_Model_Layout_Element))
#6 /var/www/demo.xyz.com/includes/src/Mage_Core_Model_Layout.php(205): Mage_Core_Model_Layout->generateBlocks(Object(Mage_Core_Model_Layout_Element))
#7 /var/www/demo.xyz.com/includes /src/Mage_Core_Controller_Varien_Action.php(345): Mage_Core_Model_Layout->generateBlocks()
#8 /var/www/demo.xyz.com/includes /src/Mage_Core_Controller_Varien_Action.php(270): Mage_Core_Controller_Varien_Action->generateLayoutBlocks()
#9 /var/www/demo.xyz.com/includes/src/Mage_Adminhtml_Controller_Action.php(263): Mage_Core_Controller_Varien_Action->loadLayout(NULL, true, true)
#10 /var/www/demo.xyz.com/app/code/core/Mage/Adminhtml/controllers/System/ConfigController.php(91): Mage_Adminhtml_Controller_Action->loadLayout()
#11 /var/www/demo.xyz.com/includes/src/Mage_Core_Controller_Varien_Action.php(420): Mage_Adminhtml_System_ConfigController->editAction()
#12 /var/www/demo.xyz.com/includes/src/Mage_Core_Controller_Varien_Router_Standard.php(250): Mage_Core_Controller_Varien_Action->dispatch('edit')
#13 /var/www/demo.xyz.com/includes/src/Mage_Core_Controller_Varien_Front.php(176): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#14 /var/www/demo.xyz.com/app/code/core/Mage/Core/Model/App.php(347): Mage_Core_Controller_Varien_Front->dispatch()
#15 /var/www/demo.xyz.com/app/Mage.php(640): Mage_Core_Model_App->run(Array)
#16 /var/www/demo.xyz.com/index.php(98): Mage::run('', 'store')
#17 {main}