I'm having a similar problem. What i've figured out so far is that the user would have to be registered with author privileges (at a minimum) in order to submit a new forum. Authors, editors and publishers are supposed to have a User Menu visible to them when they log in which would enable them to create a forum, but it's not working for me.

Sorry I'm not much help.

Is there someone else out there that has succesfully accomplished adding forums from the frontend?

Thanks!
M