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');
Thanks for the report Michel!