Check that your system directory is writable for your web server.
It needs to be 777
Please make sure below configuration steps are followed:
1. Configuration:
Add key storage location path.
Add below lines to /system/config.php file.
define('ENCRYPTION_KEYS_DIR', '/path/to/keys/');
define('DATA_ENCRYPTION_ENABLED', true);
Change path to your specific path on your server and it has to be writable/readable only to webserver
If ENCRYPTION_KEYS_DIR is not provided, default path will be used in /system/keys/ . Important to keep these keys secure!