session_start(): Failed to initialize storage module

Just one small problem. When I run the code on AWS server I get this error:
<p>Severity: Warning</p>
<p>Message:  session_start(): Failed to initialize storage module: user (path: /app/application/cache)</p>
<p>Filename: Session/Session.php</p>
<p>Line Number: 143</p>

Any idea what this is and how to fix it? This is a brand new server setup. I am thinking that perhaps I don't have the ability to write to /app/application/cache? 

My settings in config.php are:

$config['sess_driver'] = 'files';
$config['sess_cookie_name'] = 'cisession';
$config['sess_expiration'] = 28800;  // this is 8 hours, every 8 hours the session will be destroyed and when it does the user will be logged off
//$config['sess_expiration'] = 0;    //default to 7200  In addition to this if a user doesn't have any activity in 30 minutes, they will log off via javascript_funcs.js
$config['sess_save_path'] = APPPATH.'cache';
$config['sess_match_ip'] = FALSE;
$config['sess_time_to_update'] = 300;
$config['sess_regenerate_destroy'] = FALSE;

I am using CI3

proof that an old dog can learn new tricks