If you check our stats, we are not experiencing this problem since this addon has been installed, i.e. 2 Oct 2005. If your provider has bad server configuration, we can't do anything in this case.
You can check more about tempnam
function, this error is related to it, or point your provider to it. If server fails to create a temporary file, it's a server's problem. How miniBB developers can be related to the server problems?..
Be sure also you are always having fresh version of miniBB/addons themselves, also as PHP version on your server must be up-to-date regularly. PHP versions below 5.x are out of support now, incl. our support.