Err: Major problems have been detected and must be fixed before continuing while installing Symfony 2

While:

     During the installation of Symfony2 in Linux systems (for myself, Ubuntu 11.04).
     This will throws the error while try to run the url, http://localhost/symfony2/web/config.php
     This occurs for me, when i renamed the folder after once i ran the page from different folder name.

Err:

2 Major problems
Major problems have been detected and must be fixed before continuing :
    Change the permissions of the "app/cache/" directory so that the web server can write into it.
    Change the permissions of the "app/logs/" directory so that the web server can write into it.

Solution:

    For instance,

           Restart or force-reload the Apache server once to get the rid of this problem.

    Still searching for another valid solution.