A couple add-ons use the encryption library for some security related things. One downside, if you can call it that, is that the encryption library requires an encryption key be set up within your EE config file. Ordinarily, configuring the encryption key is just prudent good sense when setting up an EE site so it’s a little concerning that you don't have one.
That said though, setting up an encryption key is easy. Just add the
below to your ExpressionEngine config.php file
(system/expressionengine/config/config.php) and you're good.
$config['encryption_key'] = "513jgTnTf3*,_v(M1>CZ5T=p%;nR|lx|M\'vLKh^u$*S46\bVh.ueWEcC`5of(:";
NOTE that the value is just a random string so feel free to modify the above to meet your needs.