Make sure you are visiting the site via www.ozcardtrader.com.au to leave feedback and not any other URL.
If its not working, post a screen shot of what you are typing into the feedback page and the error.
This system works, so i'm not sure why you're having issues.
Thanks it works now, somehow I still had it :http://ozcardtraders.com.au/community/ - with the 's' as favourtes and it links.