CP not loading on Forge Server with PHP 7
2015/12/09 15:42:38 [error] [exception.Error] Error: Class 'Twig_Cache_Filesystem' not found in /home/forge/staging.domain.com/releases/20151209154140/craft/app/vendor/twig/twig/lib/Twig/Environment.php:263


That indicates that Craft is missing some of its files.  Try re-uploading your craft/app folder with a fresh copy downloaded from https://craftcms.com.