Issue: Fatal Error: vw_XenForo_CodeEventListener::init(): Failed opening required '/core.php'

I am getting these errors after an attempt to upgrade to VW4.1
ErrorException: Fatal Error: vw_XenForo_CodeEventListener::init(): Failed opening required '/core.php' (include_path='/library:.:.:/usr/local/lib/php') - library/vw/XenForo/CodeEventListener.php:148
Generated By: Unknown Account, 8 minutes ago
Stack Trace

#0 [internal function]: XenForo_Application::handleFatalError()
#1 {main}

Request State

array(3) {
["url"] => string(66) "/349210/"
["_GET"] => array(1) {
["/threads/349210/"] => string(0) ""
}
["_POST"] => array(0) {
}
}