Excellent, good to hear you found it. Thanks.

Any chance you could help us with the above mentioned Telerik attachEvent issue?
I've Googled aroud and can see that other people are having similar issues but can't find any solution. He're someone having exact same DNN problem posted on Telerik forums but it's unfortunatelly unanswered (http://www.telerik.com/forums/breaking-change-to-support-ie-11)

Basically as I understand it Telerik.Web.Ui.WebResource.axd JS functions 'hook up' to form postbacks and execute the following code:

case "pageRedirect":
                            if (m && parseFloat(m.content) >= 4) e.content = (e.content);
                            if (Sys.Browser.agent === Sys.Browser.InternetExplorer) {
                                var k = document.createElement("a");
                                k.style.display = "none";
                                k.attachEvent("onclick", H);
                                k.href = e.content;
                                h._form.parentNode.insertBefore(k, h._form);
                                k.click();
                                k.detachEvent("onclick", H);
                                h._form.parentNode.removeChild(k);

                                function H(a) {
                                    a.cancelBubble = c
                                }
                            } else window.location.href = e.content;
                            return a;

where attachEvent is no longer supported in IE11 what causes an error. The attachEvent function is used quite a few times in Telerik.Web.Ui.WebResource.axd

 Is there any way you could help us with that too?

Cheers,
Lukasz