I have pretty much what y'all have above, TeraStation with 2.14, Vista Ultimate. On another forum I saw someone suggest that I use
Username = Everyone
Password = Admin
When prompted during the backup to network process. I figured this was just to solve the silly credentials problem (I had that too, and fixed it seperately) but in fact THIS ALSO SOLVED the "Cannot create a file when that file already exists" 0x800700B7 problem. I have no idea why, and can think of all sorts of reasons why it shouldn't, but it worked.