On some configurations the database update shows a redirect url to continue the update like it should. But the redirect url is wrong! It links to an file in the forum root which does not exist (at least not in a standard installation of phpBB). ("test.php")

In line 268 in database_update.php:

echo '<a href="' . append_sid($phpbb_root_path . 'test.' . $phpEx) . '">' . $user->lang['DATABASE_UPDATE_CONTINUE'] . '</a>';