1. Do you have autoheight feature on?

2. Do you see any javascript errors on the page?

3. Is there an external link I can view your page on?

Since autoheight is not on, the problem must be with your inner page. Without autoheight, the iframe tag is a very simple tag - just loads the page into a "box" with predefined size.

Try and see if your aspx page, that you are trying to load into iframe causes some kind of errors under some conditions that makes it not come through in IFrame window.