This is because PowerCMS also includes security assist users to authenticate.
you can get around the issue by saving a copy of the WA_CMS.php as WA_CMS2.php
in the WA_CMS2.php file, comment out the line to include the security assist helper:
//require_once( "../WA_SecurityAssist/Helper_PHP.php" );
and use the WA_CMS2.php file on the security assist pages.