If you have FTP access, download /phpbb_seo/cache/phpbb_cache.php and edit it with e.g. Notepad++ - It's pretty self-explanatory what to change (for example 'url_rewrite' => true, to 'url_rewrite' => false,). Then reupload it and clear the board cache.
I install and configure phpBB-SEO (and other mods) for a fair price and very fast. If you are interested simply send me a private message.