a:4:{i:0;s:56:
"Mage registry key "_resource_helper/core" already exists";i:1;s:1486:"
#0 /var/www/velenka.com/public_html/app/Mage.php(223): Mage::throwException('Mage registry k...')
#1 /var/www/velenka.com/public_html/app/Mage.php(563): Mage::register('_resource_helpe...', false)
#2 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(534): Mage::getResourceHelper('core')
#3 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/Resource/Db/Collection/Abstract.php(520): Mage_Core_Model_Resource_Db_Collection_Abstract->_prepareSelect(Object(Varien_Db_Select))
#4 /var/www/velenka.com/public_html/lib/Varien/Data/Collection/Db.php(566): Mage_Core_Model_Resource_Db_Collection_Abstract->getData()
#5 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/Resource/Website/Collection.php(137): Varien_Data_Collection_Db->load(false, false)
#6 /var/www/velenka.com/public_html/lib/Varien/Data/Collection.php(729): Mage_Core_Model_Resource_Website_Collection->load()
#7 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/App.php(634): Varien_Data_Collection->getItemById('0')
#8 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/App.php(466): Mage_Core_Model_App->_initStores()
#9 /var/www/velenka.com/public_html/app/code/core/Mage/Core/Model/App.php(349): Mage_Core_Model_App->_initCurrentStore('', 'store')
#10 /var/www/velenka.com/public_html/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#11 /var/www/velenka.com/public_html/index.php(87): Mage::run('', 'store')
#12 {main}";
s:3:"url";s:1:"/";s:11:"script_name";s:10:"/index.php";}

<model><![CDATA[mysql4]]></model>

rm -rf var/cache/