Phatman recently made this post that works for me. Once you run this simple one line terminal code, the Terastation Pro will mount normally. As I note below, I don't know what, if any, security implications there are to doing this, but I'll try to find out. A networking specialist I know says it just involves the level of encryption, so should not be a concern (unless you're worried about that).
From Launchpad, open Utilities folder, launch Terminal. Type or paste in this.
sudo sysctl -w net.smb.fs.kern_deprecatePreXPServers=0
Press the Enter/return key. You'll get prompted for your password. Enter it (it looks like nothing is being entered, but it is) and press Enter/return. If successful, it will show that that flag has been reset from
1-->0. You're done, quit Terminal.
Apparently, you have to do this every time you reboot the computer, as it goes back to the default. Not a big problem unless you reboot a lot.
If you wish to reverse and go back to as it was, do the same, but type
sudo sysctl -w net.smb.fs.kern_deprecatePreXPServers=1
as noted above.
Amazing! After simply running that code line, my Terastation Pro mounts just like it used to.
If I'd known that 4 months ago (if, say, as good customer service Buffalo had told us), it would have saved me maybe 30 or 40 hours.
Apple presumably did this for a good security reason. The worsening virus/ malware situation on the Windows platform is what led me last year to abandon the last of my Dell equipment and switch totally to Mac.
Of course, in the process, I've lost most of my trust of Buffalo, and am less inclined to trust the Terastation for mission-critical files. It is amazing that a company like Buffalo is so tone-deaf as to handle this so badly.
