Since powerCMS was built using a previous version of SecurityAssist they aren't perfectly compatible. However I can give you instructions on how to update powerCMS code to make it work properly. There are basically two steps:
1) do a search site wide and find and replace: WA_SecurityAssist/Helper_PHP with: webassist/security_assist/helper_php.php
2) Then you need to combine the two files:
WA_SecurityAssist/helpergroupsrulesphp.php and webassist/security_assist/helpergroupsrulesphp.php
If you send me a copy of those two files I can help you combine them. Those two steps would basically update powerCMS to use the latest version of SecurityAssist so that they would be compatible.