The setup told me to rename tables for safety
I'm confused, 'cause I don't know where did you get this point? Setup script, I mean _install.php, is not telling such things.
It's said only in Manual. So if you have read Manual before, that's really great. But then you should fully follow all manual guides
before installation :) Guides in "Setting up the software: Step #1"
section carefully describe all actions that should be completed.
I guess you could have the error above described, because first
you have installed miniBB, after
you renamed tables in setup_options.php. But this step must be done before
the installation. If you rename tables in setup_options.php later, you should also rename tables in database