After trying to upgrade to 3.6 I get this error:
Not Found
The requested URL /fcgi-bin/php7_wrapper.sh/moodle/index.php was not found on this server.
Any clues?What's the operating system / hosting?
What did you upgrade from? How did you do it?
What's in the web server error log?
Is it true - if you go to that path in your file browser (or whatever you have) is it there?