I confirm this bug. I hacked around this morning some with the ExtJs code trying to fix it but wasn't successful. Its some interaction between ExtJs and NeatHtml (which protects against cross site scripting)

If I remove NeatHtml from RSSAggregator.ascx it also fixes it, but then you are not protected if there is malicious content coming in from the feed.

To see what I mean change this:

<NeatHtml:UntrustedContent ID="UntrustedContent1" runat="server" TrustedImageUrlPattern='<%# allowedImageUrlRegexPattern %>'
ClientScriptUrl="~/ClientScript/NeatHtml.js" Visible='<%# ShowItemDetail %>'>
<%# DataBinder.Eval(Container, "DataItem.Description").ToString() %>
</NeatHtml:UntrustedContent>

to this:

<%# DataBinder.Eval(Container, "DataItem.Description").ToString() %>

and it works.

Strangely, forumthreadview.aspx also uses NeatHtml but it doesn't throw this error. Apparently there was a report for a similar error in ForumThreadView.aspx back in June. According to the thread I fixed it there but I can't remember for the life of me what the problem was or how I fixed it and comparing the code in both places doesn't reveal anything different that I can see.

I consider the extjs-viewport1 skin kind of experimental

Best,

Joe