getting a button in a parent frame to click automatically when a button in an iframe is clicked

How can a button clicked with a mouse inside an iframe automatically click a button in the parent frame ?
Using VB and Javascript, have got simple Javascripts in the iframe to run in the parent frame from a button click in the iframe, alert()s and setting focus to form elements in parent, but get error when trying to set focus to parent frame button, "unable to get value of the property 'focus':object is null or undefined. The others work ok.