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

I am working on Symfony project.

When i try to do :

php app/console cache:clear

i get the following ErrorException:

Warning : rename (../app/cache/dev , ../app/cache/dev_old ) : Access Denied . (Code : 5) in ../vendors/Symfony/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php on line 76

What is the problem here? I have given all permissions to the user on my machine (Windows 7 OS). Any ideas why it is happening?

Thank You.