When you get page faults go to MS Knowledge Base and copy the error message into the search form. Select full search and you almost always get a result that helps. How much it helps is the real question. Here is what you get for that error under the cause section.
---- Copyed from MS Knowledge base article Q265244
This can be caused by an XML file that uses an XSL file to create either an anchor tag (A) set to change the right frame or element that calls Window.open ("URL", "rightframe").
This only happens if the right frame is currently pointing to a page located on another domain. If the page is on the same domain, it works fine until the page changes to a separate domain.
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I don't know if that's any help but threads is using xhtml. I'm betting that Miscrosoft uses an XSL file to translate xhtml into html before putting it into the Modzilla engine.
With that in mind you might want to check into the templates and make sure your html is good xhtml. You can also tell your users to upgrade when they complain.