I discovered that NikonView as well as my card reader were not working after installing Windows Critical Update 'KB908531' a week or so ago.
Nikon Tech Support found the Microsoft problem in a tech note on the MS web site.
Apparently Windows Explorer and a number of 3rd party software products won't work after installing this upgrade if you have certain HP and/or NVIDEA hardware.
The MS fix is here:
http://support.microsoft.com/kb/918165
Nikon thinks that MS may have a better fix by the end of the week.