There is below information in the log, but no idea what could cause this :(
a:5:{i:0;s:45:"Unable to read response, or response is empty"; i:1;s:1003:"#0 lib/Varien/Http/Client.php(61): Zend_Http_Client->request('GET')
#1 app/code/core/Mage/Adminhtml/controllers/DashboardController.php(100): Varien_Http_Client->request('GET')
#2 app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_DashboardController->tunnelAction()
#3 app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('tunnel')
#4 app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#5 app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#6 app/Mage.php(684): Mage_Core_Model_App->run(Array)
#7 index.php(83): Mage::run('my_store', 'store')
#8 {main}";
s:3:"url";s:543:"/index.php/admin/dashboard/tunnel/key/ba90f30f2af450c5980c4c6353c49d61/?ga=..&h=..";
s:11:"script_name";s:10:"/index.php";
s:4:"skin";s:5:"admin";}