Thanks David! But (nothing too bad): the store patch created errors and a reject file (==> acp_database.php.rej), no idea why. I made those changes manually then.
I used the install folder from the original 3.0.4 tarball.
*************** *** 26,32 **** function main($id, $mode) { global $cache, $db, $user, $auth, $template, $table_prefix; - global $config, $phpbb_root_path, $phpbb_admin_path, $phpEx; $user->add_lang('acp/database'); --- 26,32 ---- function main($id, $mode) { global $cache, $db, $user, $auth, $template, $table_prefix; + global $config, $phpbb_root_path, $phpbb_admin_path, $phpEx, $url_forum; $user->add_lang('acp/database'); *************** *** 530,537 **** if ($store == true) { - global $phpbb_root_path; - $file = $phpbb_root_path . 'store/' . $filename . $ext; $this->fp = $open($file, 'w'); --- 530,537 ---- if ($store == true) { + global $phpbb_root_path, $url_forum; + $file = $phpbb_root_path . 'store/'. $url_forum. '/' . $filename . $ext; $this->fp = $open($file, 'w');