Cannot connect remotely to router. Incorrect username or password

My router Zyxel VMG8823-B50B with last firmware works correctly in LAN. Usually I access with admin user.
Iv'e enabled the remote connection (on port 80) and I see correctly the console at my dynamic address (done with no-ip).

But when I try to login remotely with admin user i receive the incorrect username or password message (In italian: 
Il nome utente o la password non sono corretti.).

What's wrong?

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