If you look at the error, you will see the problem is actually with the help module. The problem is the Help module is referencing a specific version of the webcontrols project and the one you are using on your site is a different version. I would look to see that you have the latest version of Help installed.

The past 3 days were around the help module and now you are reaching the forum module frustrations :)

If you give registered users role edit rights to the module and you don't assign any values for authorized, authorized edit roles (thus making a forum private) in the edit forum, this will work as expected. This is a bit diff from other DNN modules and I have already starting making a change to keep this from happening.

I don't know your persmissions schema, nor do I know anything about your site. Here is what you need to keep in mind:

The module has permissions settings that must be set. How you set these depends on who needs to see and who needs to post on the module. You also have tab permissions here to be worried about who can see. So, if a role can see the tab they can usually see the module. Whoever you want to be able to post in the module, if they can see it, regardless of private forums needs to have edit module permissions on the module. Remember, this needs to account for all forums within all groups shown by this module. If you need further restriction (maybe one forum is open for registered user posting, another only for 'special' role posting or viewing) you then need to restrict each individual forum further using private forums and authorized edit and view roles on the specific forum.

Edit module permissions on this module are not ADMINISTRATOR permissions, this module is very different. Another thing, people can ONLY edit their posts if they are moderators, administrators or trusted users.

The module does what you want it seems you are just having some issues understand what settings to change. Please read the documentation available for download from the project's download page.