Symfony Warning : rename (../app/cache/dev , ../app/cache/dev_old ) : Access Denied . (Code : 5)

Be sure that the files are not in use (as meze pointed out). If you're using something like TortoiseGit or Netbeans, etc - be sure to mark the cache folder as ignored so that they are not accessed.

If all else fails, download a free program like Unlocker that will allow you to quickly and easily detach running processes from the files/folders you are trying to modify.

To expand on leek's post, Symfony 2 cache-clearing operations shuffle the cached items across different folders during the cleanup. Part of this process includes creating cache/dev-new/ and cache/dev-old/ folders.

If you are using Eclipse or another IDE that dynamically monitors subfolders within your project, the IDE will nearly instantly spot the new folder creation and look in those folders for new files (in Eclipse, I noticed the DLTK module constantly doing this in the Progress View). This may unfortunately get in the way of Symfony, which wants to rename and/or delete these folders.

Specifically with Eclipse Indigo on Windows 7 64-bit, you can remove the cache/, cache/dev/, cache/dev_old/ and cache/dev_new/ folders from the build path by right-clicking your project and selecting "Build Path > Configure Build Path...". This originally had no effect for me; I kept seeing the DLTK module trying to index the cache folders. I ended up uninstalling the Aptana Studio plug-in, closing all Editor documents, shutting down Eclipse, manually deleting the sub-folders in the cache/ folder, running Symfony cache:clear, then starting up Eclipse and reinstalling Aptana. Seems to have worked thus far.

It's an issue with Symfony 2.0.x and Symfony 2.1.x. These a workaround for this:

Open the file: src\Symfony\Bundle\FrameworkBundle\Command\CacheClearCommand.php

and add the statement sleep(1); where the directory creation is failing, in the execute() function:

    //...
    rename($realCacheDir, $oldCacheDir);
    sleep(1);
    rename($warmupDir, $realCacheDir);
    //...

You might have to re-open the CLI twice and run cache:clear, but it will fix the problem after that