Think you have to remove the device from the device list, is done in the devicemanager, see http://articles.techrepublic.com.com/5100-10878_11-6017628.html for the details (and you may skip the commercial 
Thanks. i fired up the device manager and selected View->Hidden Devices. The list included one with a suspicious yellow exclamation point and when i right clicked it told me the drivers were uninstalled for this serial device. I clicked on the Update Drivers button and the resulting Update Drivers wizard allowed me to select the Arduino drivers file. Proceeded with installing drivers and everything worked fine incl. the Blink example.