Turn off the add-on in the ACP and uninstall, if that doesn't work, edit the config.php file and add the following line:
$config['enableListeners'] = 0;
The forum should now work, but no add-ons will. Try uninstalling the add-on now if you couldn't before, then remove the above line from config.php
I just want to make sure I'm in the right place but this is the config.php that should be located in community/library/ correct? If so I have added the line (and did a the upgrade again) and it did not work.
I'm afraid that when I installed this add on I was asked to overwrite a file in the library (possibility the index.html, which is only 1byte now). Not sure if this could be a potential problem.