It sounds as though your iframes are using different domains. All major browsers block access to parent iframes if they are not using the same domain. IE if you have the domain www.test.com and you embedded a page from www.google.com and try to access/modify anything from google's website, you will be denied access.
The other answer to this question explains the implemented API post message. This can also be used to send/receive data from different frames from different domains. However, the things you can do with that are limited compared to if you had two frames using the same domain.
That being said, here is the answer if your iframes are using the same domain.
window.parent.observer;
Hope this helps someone :)