Could check to see if XMLRPC is working on your server. Download http://ourcommoninterest.org/downloads/xmlrpc-sayhello.zip which Burtadsit wrote.
And to steal some words from Lance Willett:
The test consists of two files. The first file is a bbPress plugin that you activate in the bbPress plugins area that acts as a XML-RPC server and responds to a simple “say hello” type call. The second file goes in the root of your MU setup.
This test bypasses all the “bbpress_live/discover_pingback_server_uri()” stuff that might be giving you problems. If this works then the issue is most likely in that area and could be a host/server problem.
To load the test, first install the “oci-bb-sayhello.php” file to your bbPress install root in a folder called “my-plugins” (create the folder if it doesn’t exist). Then log into bbPress and activate the plugin. Next, drop the “oci-bp-sayhello.php” file into the root of our MU install so that you can navigate to it easily. Then load “your-site/oci-bp-sayhello.php” in a browser and see what the output is.
Thanks for the quick reply and the debugging options!
This is the result:
“-32300 >> transport error – HTTP status code was not 200”
I guess that is not good. 
xmlrpc.php is reachable and returns 200 on a GET (although it seems to require POST)
I just noticed that every attempt to post something in any (non-group) forum leads to a screen filled with the following error message:
Warning: cannot yet handle MBCS in html_entity_decode()! in /[path to bbpress]/my-plugins/buddypress-enable.php on line 53
I could fix the last error by switching to PHP5.
The sayhello test and the group forums are still not working, though. 
Florian, if the test isn’t working, then the group forums ain’t gonna work.
You need to confirm with your host that they support remote procedure calls (and XML-RPC specifically)? It might be that they are not allowing remote calls to be made to the same server.
And try reading burtadsit’s post here.
I contacted my host about the problem and they could indeed fix it. Everything is working fine now.
Thanks a lot!
Hello,
I did ALL you say, even trying “xmlrpc – Say hello from bbPress” plugin, and I received the “Hello from bbPress!” msg but Forums dont work, no way, i am desperate, i have tried bbpress alpha 6 rc1 rc2 rc3, i am just out of ideas.
Can you tell me what more i could check in my server? i tried same procedure in other server and it works ! but its not my server, and in mine no way … phpmemory is 64 mb so…
i have tried for 5 days…. right now there is integration of users, if i log in wp mu I am also imn bbpress but i dont have “enable forums” options, i have the infamous ” Attention Site Admin: Group forums require the correct setup and configuration of a bbPress installation.”
@notme31
Are you having the same issue as the original poster? If not, you should start a new thread as this thread is marked as resolved and few people will pay attention to new support questions in resolved threads.
