There is one thing that I know of that can cause this problem. Have you updated any of the Security Assist files in the PowerGallery area? The version of the HelperGroupsRulesPHP.php file that is included with PowerGallery differs from the one that would be created if you ran Security Assist or one from another solution. You should try re-uploading the original version of this file after making a backup of the current version to see if this resolves the problem.
I have opened a ticket for you on this issue in either case. If you can resolve the problem by re-uploading this HelperGroupsRules file there is no need to respond to the ticket. If that does not solve the problem for you then you can add to the ticket by logging in and going to your support history.