HTTP 500 ERROR after upgrade from 2.21 to 2.3

I've made 3 previous release updates without issues but ran into one now. I've uploaded the 2.3 files overwriting existing vanilla files.folders, deleted .ini files in /cache and now the url just http 500 errors on homne page and utility update page. Also tried removingextra plugin and application lines from config.php Help please?

[error] 1963#0: *2383 FastCGI sent in stderr: "PHP message: PHP Fatal error: require_once(): Failed opening required '/srv/beta/vanilla/vendor/autoload.php' (include_path='.:/usr/share/php:/usr/share/pear') in /srv/beta/vanilla/bootstrap.php on line 50" while reading response header from upstream, client: 123.456.789, server: blah.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/var/run/php5-fpm.sock:", host: "blah.com"

The path and file exists: /srv/beta/vanilla/vendor/autoload.php

PHP 5.5.9-1ubuntu4.21