Strange error every time saved in log file

[activestate10]

2013-09-03 13:30:27 Error: [MissingActionException] Action AppController::webroot() could not be found.
Exception Attributes: array (
'controller' => 'AppController',
'action' => 'webroot',
)
Request URL: /cakecms/app/webroot/thumb/p7.png
Stack Trace:
#0 D:\XAMP\htdocs\cakecms\lib\Cake\Routing\Dispatcher.php(187): Controller->invokeAction(Object(CakeRequest))
#1 D:\XAMP\htdocs\cakecms\lib\Cake\Routing\Dispatcher.php(162): Dispatcher->_invoke(Object(AppController), Object(CakeRequest), Object(CakeResponse))
#2 D:\XAMP\htdocs\cakecms\app\webroot\index.php(110): Dispatcher->dispatch(Object(CakeRequest), Object(CakeResponse))
#3 {main}