Final update (hopefully!):
I am finally back to normal (I think...).
For the benefit of all I just want to list the steps needed to get me back. Starting with the status from my last post ("TS-TGL-EM" with IP = 192.168.1.105):
1) used following nasupdate.ini file I ran NASUpdater.exe:
[Application]
Title = BUFFALO TS-TGL Updater Ver.1.04
WaitUpdate = 200
WaitReboot = 100
WaitFormat = 240
[Target]
ProductID = 0x2002
Name = TS-TGL-EM
Password=password
[Flags]
VersionCheck = 0
[SpecialFlags]
Multiple = 1
Quit = 0
Debug=1
Using debug mode I checked all boxes ("Ignore Current Version", "Format Completely", "Clean User Area"). ***Warning: it appears that these settings delete all data, and sets Raid array to spanning mode - only do this if you have first transferred all your data to another location off of the TS.
The firmware process started without issues. At the first restart of the TS I got the "TS-TGL-EM can't respond for 100 seconds - Retry again?" error message. This is because after restart the IP address on the TS was for some reason set to "192.168.11.150". I manually restarted the TS (in EM mode with the reset button) and the TS now rebooted to "192.168.1.105" (evidently router assigned by DHCP).
I then clicked the "retry" button in the NASUpdater.exe application and the firmware upgrade process continued. The large file (~ 40 MB) transfer proceeds and all looks OK until the next restart of the TS. After restart the TS is yet again set to IP "192.168.11.150" and the name has been changed to "TS-TGL261". Of course, I get the same "TS-TGL-EM can't respond..." error message (name change and IP address change). I maually restarted the TS (in EM mode) again and the TS rebooted to "192.168.1.105" - but this time the TS was now web interface accessible.
However, when accessing the TS ("TS-TGL261" with IP = 192.168.1.105) all the webpages are in Japanese! No - I can't read Japanese - I just was lucky to have another TS which I could refer to to figure where to change the language settings. On the basic page (2nd in the list on the left) I changed:
1) name: to "TS-TGL-EM"
2) display language: English (2nd item in the drop down list)
3) windows client language: CP437 (2nd item in drop down list)
When I clicked the "apply" button (bottom of page) all Japanese characters changed to English so that I could at least read the configuration pages again.
Now that the TS name was again set to "TS-TGL-EM" I went back to the NASUpdater.exe application and clicked "retry". This time the application found the TS on the network and reported back that the firmware update was successful. So - forced firmware upgrade complete but with some workarounds!
Going back to the web interface I reset all my configurations (static IP address, name to "TSP-ATLHOME", etc.). I also found that the RAID array 1 was reset to spanning mode so I deleted the RAID array 1 and reconfigured all four hard drives into a new RAID 5 array.
As I write this the TS is now going through the process of scanning the newly created RAID array (all drive access lights flickering and display shows "I17 RAID array 1 resyncing" message - probably will take hours to complete this as before. However, all seems to be in working order. I can access the TS though my network (ping and web interface) and the I12 degrade error message that started this whole thread no longer appears in the display. Of course I will still have to transfer all data back up to the unit when the RAID array setup is complete.
I hope this is the last you will hear of this problem. I don't know if what I observed is typical or is symptomatic of a problem that is still lurking in the background. If something is still wrong I'm sure I'll be back with more questions.
Thanks to all who helped get me this far. I hope what I experienced was not entirely unique so that it may help others who may have problems with their TSs.