Undeclared method 'x' in class 'y'

Sample code:

//...
class y {
    function xx() {
        //...
    }
}
//...
$obj = new y;
$obj->x($args);     // Undeclared method 'x' in class 'y'
//...

You tried to call method on object of some class that doesn't have appropriate method declared. Please note that Codenizer will not check for nonexisting methods of classes that implement __call method.