Get form hidden variable value from outside the IFrame

An iframe contains a form with a hidden variable (input type =" hidden">and I needed to access this hidden variable in the parent page which contains the Iframe, here is how I did it:

http://pietschsoft.com/post/2004/08/12/JavaScript-How-to-get-value-from-nested-form-in-iframe.aspx

but it didnt work for every website, on some it gave the javascript permission denied error:

http://support.microsoft.com/kb/167796