There are a handful of potential problems in that version. The solution right now would be to edit vars_misc.cgi... find the line reading "BBStatus" and change the value from "ON" to "OFF"
Then immediately rename cp.cgi, so the user can't get back in to the board.
Report back here when you've done that. Next, you'll be shown how to create a new admin user... and after that, you get to upgrade to 6.6.