Cannot create new users

I’m not sure if this is the right category as my EX2 Ultra is still on V2.41.116 (update doesn’t work, but that’s a different topic).
Anyway, my problem is that I can’t create new users. When I go through the “add user” process, the new user is shown under users. But as soon as I leave that tab, the new user disappears. If I return to the user tab only the initial “admin” user is there.
Sometimes I get an error 400056 (user name not found) when I create a new user, but not all the time.
Anybody any idea?

Hello,

Please refer to the following KBA article: http://support-en.wd.com/app/answers/detail/a_id/30052/