When logged in as Administrator and trying to delete a Reply from a Topic by clicking on the 'Delete Reply' icon I see a blank popup window appear for a few seconds after which it closes having no effect on the Reply. The same effect is present with both MI6 and Mozilla Firefox. Why does this happen?
It is probably a verification page that is getting called. Like pop_delete.asp or something. Maybe the document has become corrupted somehow. When the pop up happens, try to see what it is though your task manager