I did download the Moto driver but no luck. BTW, the Droid shows up in Device Manager as a disk drive working properly. Go figure. Thanks for your assistance.
Not sure if you are still having the problem, but I ran into the same issue with my Windows 7 (64 bit) computer and my Droid. Here's the workaround that I have to deal with each time I want to mount my SD Card to my computer:
1. Open Device Manager (Make sure Droid IS NOT plugged in for this to work)
2. In Device Manager, click View then Show Hidden Devices
3. Click on Storage Volumes to expand the list
4. Uninstall all hidden Generic Volumes (these are the lightly grayed icons)
5. Plug in Droid and go through the typical steps to mount the SD Card and you should be good to go.
6. As always, make sure to safely remove before unplugging USB cord once done.