Thanks for the help, Wildstar. I checked the Registry, but found it was pointed to the correct drive letter.
However, that got me thinking. I had loaded the game from my second optical drive (drive E: ). So I uninstalled, then reinstalled with the disk in the D: drive. And, by gum, it worked.
My belief is the game code ALWAYS looks to the D: drive, despite what Windows has in the registry. So there you have it!