I think you should upgrade your forums, or even better use Compiler
, compile your version (which will include all add-ons installed *properly*) and re-design your forums for this version. Of course this all can be done keeping your current database and users.
It's not good to keep an outdated software. Within couple of years we've had lots of changes, and the file upload add-on's recent release will work only with miniBB version 2.4 and higher
, as it's stated in readme.txt.
Here's how to know out the miniBB version