That plugin is no longer supported by the new versions of Q2A not being updated.
Why don't you use the Q2a Core system cache.
You find it in the administrator menu of Q2A version 1.8.3
You just have to create a directory for the file system cache to work for you.
And modify in your file qa-config.php
adding the line
define ('QA_CACHE_DIRECTORY', 'cache');
For example I have a directory named cache in the root of my site
And it is the one that works as such with Q2A