Hi there!
Just an update on the topic available at https://moodle.org/mod/forum/discuss.php?d=442070#p1777939, because it is closed but without the answer.
In my case, I had the same error: Error, unable to load libraries
Searching in my config.php, found out some old debug code still enabled....
Trying different configurations, found out that the two lines responsable for the error are:
If you really need, you can let the other lines enabled, because the error is gone anyway.
Hope this helps someone.
Regards!