Parser.php "PHP Fatal error:  Call to a member function addBlock() on boolean"

`PHP Fatal error:  Call to a member function addBlock() on boolean in /var/www/html/csstuff/lib/Parser.php on line 746`

I am trying to figure out what is triggering this and and how to avoid it. It says "on boolean" so I am wondering if it triggers if the block is on line 0/1? 