Well, I solved my own problem (while I was on hold on the phone with Buffalo Tech Support). I'll post the resolution in my case. The problem was that my Linkstation was not getting an IP address assignment from the DHCP server in my router. i don't know why since this had been working fine. I confirmed that the MAC address that I specified for the router DHCP reservation list for my router was correctly specified
Using the default IP address for my LinkStation (192.168.11.150) I was able to use the configuration pages to manually assign an IP address to my LinkStation on my home network.
After assigning the IP address life was good again. Windows drive mapping works, FTP access works and the HTTP web admin interface works. Everything back to normal -- no configuration settings or data lost.
I must have a router glitch (aka bug). I did power cycle my router and network switch when I first saw this problem. But, that did not correct the problem.
For what it's worth my router is a LinkSys E3000 and I use a Netgear FSM700S network switch in my home network. Since I have things working satisfactorily for me now, I don't care to pursue this any further.
This post is like talking to yourself -- but I hope it will help someone else.