I had this problem and have finally solved it.
Here’s what I did:
1. deactivate all plugins except buddypress
2. change theme to default
3. backup your bb-config.php file
4. delete bb-config.php
5. backup /public_html/wp-content/plugins/buddypress/bp-forums
6. rename /public_html/wp-content/plugins/buddypress/bp-forums
7. download the latest version of Buddypress
8. upload new version of /public_html/wp-content/plugins/buddypress/bp-forums
9. upload rest of the latest version buddypress files
10. go to your dashboard >Buddypress > components >forums click to install group forums and it will create a new bb-config.php file
11. create a new group – DO NOT SELECT ENABLE DISCUSSION FORUM
12. save the group
13. go back into the group and select enable discussion forum
14. create a new topic for your new forum
15. If it works – check the other groups.
16 If the other groups don’t work – de-select enable discussion forum and save – then select discussion forum and save again – see if that helped.
17. change to your custom theme – double check again. You may need to redo step 16 for some of your groups
18. reactivate your plugins and check again – you may need to redo step 16
I know that seems like a lot of steps – and possible you could skip some of them – but that’s the exact process I used and it worked… woot!!
Good luck
Stef
@inweb thank you for sharing your solution to current WP 3.3 and BP 1.5.2 forums. However, this thread is more than a year old and solution was different. Closing this thread.