Internet Explorer has a peculiar behavior in handling cross frame scripting when different security zones are involved.

Whenever two frames that communicate one with each other are located on two different servers (e.g. and, as happens with Lightstreamer web client library when the "External Deployment" approach is used) and those two servers are registered in two different IE's security zones, even if the document.domain property of the two pages is changed to be equal, the communication is not possible and a "permission denied" error is thrown.

The solution for this issue is to configure both servers to be in the same security zone on the client IE:
go to Tools->Internet Options, then click on the Security tab.
There you can select one of the zones, then clicking on the Sites button you can easily configure the list of associated hosts to make the web server and the lightstreamer server live in the same security zone.

This issue was seen on IE6 IE7 and IE8.