"You need to login"

When trying to login to the admin section of Joomla you receive the error "You need to login" even when you enter the valid user and password.

This is generally related to the application unable to write to sessions.  

In order to fix this you need to modify the configuration.php file located in your joomla directory on your server.

Add the following line to the bottom of your Joomla configuration.php, but before the ?> at the end.  Make sure to modify the path to a writable directory. 

session_save_path('/path/to/joomla/sessions');