PHP Fatal Error after Update

When I update to the latest version of backwpup, I get the following PHP Fatal Error:

PHP Fatal error: require(): Failed opening required ‘/wp-content/plugins/backwpup/vendor/composer/../guzzlehttp/promises/src/functions_include.php’ (include_path=’/wp-content/plugins/backwpup/vendor/pear/archive_tar:/wp-content/plugins/backwpup/vendor/pear/console_getopt:/wp-content/plugins/backwpup/vendor/pear/mail_mime:/wp-content/plugins/backwpup/vendor/pear/net_url2:/wp-content/plugins/backwpup/vendor/pear/pear-core-minimal/src:/wp-content/plugins/backwpup/vendor/pear/pear_exception:/usr/local/phpbin/PEAR/:./’) in /wp-content/plugins/backwpup/vendor/composer/autoload_real.php on line 70