When you say the add sign never appears you mean it wont let you release the file into the drop area? Odd. I just checked it out on a Windows 7 machine here running v2010 and it seemed to work ok. Maybe it could have something to do with admin rights? Could you try logging on as an admin and seeing if that helps? Perhaps also dragging other files (e.g., from your desktop and see if the problem is limited to specific files)?