Success! Thank you for your swift, detailed, easy-to-follow, and thorough reply.
Because it might help with future troubleshooting for other users, here's some notes on what I did:
First, I followed the instructions in the first three sections of your reply and found that all of my settings were already as you recommended.
Next, I followed the instructions in your fourth and final section. Background: I already had the shared volume in the folder list. I had added it before I contacted you and things weren't working. I had added it by browsing and clicking in the "Browse for Folder" window that pops-up when you click the Add button. Since I knew that method wasn't working for me, I used the Remove button to remove that instance from the list. Then I followed your method of manually typing the drive letter in the Folder field at the bottom of the "Browse for Folder" window (in my case, Q:). This added Q: to the list (and it was the only item in the list).
BUT, this wasn't working either -- at least I believe it wasn't working (maybe I didn't wait long enough for the index to populate).
Anyway, I removed that instance from the list and then tried again the method of browsing and clicking on the desired item. AND HERE'S THE KEY THING: This time when browsing the tree in the "Browse for Folder" window, I realized I had taken a wrong turn when I originally added an item to the list. I had mistakenly browsed under NETWORK and found my NAS server name and under that the shared folder I wanted to index -- I had clicked on that. BUT THIS TIME, I browsed under COMPUTER and located the drive I had MAPPED to the NAS server and now I clicked on that. And that's when everything worked. I now realize that makes much better sense than what I did originally -- and I'm a little embarrassed to admit it.
That was a long explanation so let me bottom-line it: When selecting the desired item for indexing in the Browse for Folder window, I should have browsed under COMPUTER and selected the drive I had mapped (and NOT browsed under NETWORK).
Hope this information is useful and I really appreciate the help you provided.
Cheers,
Huge Fan of Everything