My page have an iFrame here:

here is the code of putting the iframe:
<iframe src="" name="iframe_a" scrolling="no" width="100%" frameborder="0" style="margin-top: 200px; background-color: White;"
id="I1"></iframe>
when I click any button that triggers page load, the page keeps adding more white spaces below the iFrame:

How can i prevent this kind of problem?
NOTE:(I’m using ASP.NET)
I will appreciate all answers, advices and suggestions 🙂
The “iFrame” is not at fault. Check the source of the “iFrame”.