When running CakePHP on Heroku, by default you'll see file permission errors. The Heroku filesystem is read-only, but '/tmp' and '/log' are writable. To remove the errors update Config::config() in core.php

core.php

<?php
// Heroku Read-only Filesystem https://devcenter.heroku.com/articles/read-only-filesystem

/**
 * Configure the cache used for general framework caching.  Path information,
 * object listings, and translation cache files are stored with this configuration.
 */
Cache::config('_cake_core_', array(
  'engine' => $engine,
	'prefix' => $prefix . 'cake_core_',
	'path' => '/tmp/', # New Path
	'serialize' => ($engine === 'File'),
	'duration' => $duration
));

/**
 * Configure the cache for model and datasource caches.  This cache configuration
 * is used to store schema descriptions, and table listings in connections.
 */
Cache::config('_cake_model_', array(
	'engine' => $engine,
	'prefix' => $prefix . 'cake_model_',
	'path' => '/tmp/', # New Path
	'serialize' => ($engine === 'File'),
	'duration' => $duration
));

it works. Thanks!