An update released today (25-10-2011) may cause issues after being installed when you try to rename or move files/folders. There was another update in April 2010(?), KB980408, that caused the same issues for many people running Windows 7 64bit. So if you find yourself in this position, you know what's causing it!! Luckily, (a) Windows creates a restore point before installing KB2670576 and (b) It is an optional update, not a security update. HTH.