Re: bbMenu 1.1 programming problem (advanced!)
The errors stem from the fact that plugins aren’t designed to be called in isolation. They are included into the rest of bbPress when they are loaded. Meaning that if you try to run the plugin in isolation, then you won’t have access to the whole bbPress API (including the add_action() function and all the bbdb class).
If you take a look at how tag addition works in the core, you will probably get an insight into the best way to do this.