Silverlight in an IFrame in IE

I am having a problem with calling a silverlight 4 app from an iframe. I have a page (see below) that calls a separate program that contains a silverlight application. This seems to work fine on some computers but on other computers it ends up with a blank screen. I have tried setting explicit widths on the iframe as well as verifying that the src of the iframe is v开发者_JAVA百科alid. This seems to happen on in Internet Explorer both versions 7 and 8. It seems random which computers it works on and which it doesn't. Any ideas?

Code of the iframe page:

    <form id="form1" runat="server">
<iframe runat="server" id="mainframe" style="height: 600px; width:1024px; min-height:600px; min-width:1024px; border:0;" frameborder="0"  src="http://XX.XX.XX.XX/silverlightapp/TestPage.html" />
</form>

This is probably security related. It looks like the web page you are embedding is from another domain. Depending on the security settings on the machine, Silverlight content may be blocked within the iframe.