setPrefixedCookie: Can't set cookie, headers already sent!
The issue related to content being loaded on the page before headers were being sent, this post has a description of the issue:
I'd suggest searching the page the issue is happening on and removing any white space before the viewer_functions.php file loads.
If you can't resolve the issue, we can take a look if you raise a second level support request here:
PHP Programmer - interactivetools.com