Try leaving the workgroup then rejoining & remapping the drive. I'm thinking here that the Sid's for automatic logon have changed since the reformat, which would cause the incorrect username box to appear. When you enter it again, only the user/pwd is used to authenticate and since that exists on the server, you can log on. Leaving the workgroup and then rejoining should reset all the Sid's for the reformatted computer, allowing you to access the drive without entering a username/password. Hope that works for you.