I have the 12TB version of the WD My Cloud EX4, and I was running into the problem with the recurring “User Not Authorized 400057” error after configuring the unit and assigning a password to the admin account.
One workaround which I saw posted here was to remove the admin password, log out and back in, and then re-add the admin password again, and this worked for me for a while, but the errors would recur again after a while, and the solution never worked beyond a reboot.
I have found another workaround which so far seems to work persistently for me: Change the admin password so that it only contains alphanumeric characters and underscores. If I try to set the admin password to, say, something with a “?” or a space in it, the 400057 consistently comes back, but if I restrict my passwords to upper and lowercase letters, number,s and underscore, it seems to resolve the problem.
Since making this change, I haven’t seen the 400057 error recur, and I’ve added more shares and users and associated more cloud devices to the unit without any further problems. I wanted to share it here in case it worked for anyone else who has this issue, so please let me know if it works for you (or if it doesn’t, and I’m just chasing a red herring).