Session problem

[eluser]Gabi3xz[/eluser]
I have code

Code:

$ss_data = array(
                   'username'     => $this->input->post('email_address'),
                   'logged_in' => TRUE
               );
$this->session->set_userdata($ss_data);

A PHP Error was encountered
Severity: Notice
Message: Undefined property: Login::$session

where is the problem?
If i added session in $autoload['libraries'] have other error.

An Error Was Encountered

In order to use the Session class you are required to set an encryption key in your config file.

[eluser]weboap[/eluser]
application/config/config.php

Code:

/*
|--------------------------------------------------------------------------
| Encryption Key
|--------------------------------------------------------------------------
|
| If you use the Encryption class or the Session class you
| MUST set an encryption key.  See the user guide for info.
|
*/
$config['encryption_key'] = 'some_string_as_encryp_key';