Hello,
In our project, we are using ModalPopupExtender and it is not working using desktop IE10 running under Windows 8. Popup cannot be dragged. I have tried to use different Browser Modes (IE10, 9, 8, 7) and Document Modes. None of them worked. I have also tried to launch same application in Metro IE10 and the popup can be dragged. Also IE10 under Windows 7 was working properly.
I have checked the sample code here: http://www.asp.net/ajaxlibrary/AjaxControlToolkitSampleSite/ModalPopup/ModalPopup.aspx with same results as described.
EDIT: Our project is using .NET Framework 3.5, and AjaxControlToolkit version: 3.5.7.0123.