When $config is not set, throwing the exception :

throw new Zend_Config_Exception("Cannot find $config array in $filename");

triggers a PHP notice:

Undefined variable: config in path-to-ZF-library/Zend/Config/Array.php on line 58

my fix is to replace the double quotes with simple quotes:

throw new Zend_Config_Exception('Cannot find $config array in $filename');