I'm one of the two active developers on this product; I asked a legitimate question to you on the 26th regarding data in your webserver logs which would troubleshoot your issue.
What data displays in your site error log (possibly even the access log) when the forum gives a 403 error? It's possible that your users may be triggering a Suhosin related error.
As of your posting today, you have yet to respond with any amount of data to troubleshoot your problem and have instead taken to bashing the product instead of answering the simple request of providing data to resolve your issue.
I, like Ruben, am here providing user to user support, for free, on my own time (no one is paid for support on these forums, the only official support from the vendor is the support system).
If you cannot provide data that would be unique to your hosting configuration, there is no possible way that we can provide support to you. I can provide many ideas towards a resolution, but if you're unwilling to fulfill your end of a troubleshooting conversation, there is nothing more that can be done to provide support on your issue.
