We are using Telerik 2008 Q3. We have a page that is almost entirely inside of a RadAjaxPanel and we are using a RadScriptManager and RadStyleSheetManager in the master page.
I ran debugging on it and found that it is this line
which was in the MicrosoftAjax.js file.
I don't entirely understand what is causing this. I don't get it on my local machine or even on our test server, but I can replicate it using a PC with a fresh install of Windows XP with SP2 and IE6 against our production environment. I've found items from Microsoft suggesting that it is because of an iframe and they suggest hacking the framework to get fixed. However, we don't have any iframe on this page, and I was unable to find any when viewing the source.