IE6 incorrectly sends back exact URL given on redirect incuding # and following which causes site to respond with "unknown thread" type of error message. One suggested workaround for this known (but not particularly well) IE6 issue is http://blogs.vertigo.com/personal/tomphan/Blog/archive/2007/05/11/response-redirect-and-the-anchor-in-ie6.aspx or something like String cleanmessageid = request.getParameter("messageID").split("#")[0];