[horde] Deny log in to users from same IP address

[Juan Bernhard]

Hello list, I have a problem, and I dont know where else to look.
We have a horde webmail running from some time, I updated it some weeks
ago to version 5.2.4
Recently (yesterday) I had some users complains about login denied.
The message in the web says something like "You have changed your IP
address since the beginning of the session. For security reasons, log in
again" (this is a translation, we use the spanish version)
Of course, loggin in again gets the same message.

In the horde log I got:
Apr 24 15:10:05 webmail HORDE: [imp] Login success for esetteca
(190.221.196.248) to {imap://imap.inti.gob.ar/} [pid 19516 on line 157
of "/var/www/html/imp/lib/Auth.php"]
Apr 24 15:10:06 webmail HORDE: User esetteca is not authorized (Remote
host: 190-178-163-226.speedy.com.ar) [pid 19518 on line 324 of
"/usr/share/pear/Horde/Registry.php"]


All users from the same IP addres (remote office behind a PAT) get this
message.
I don't have any permission or limit configured to deny log in, in a per
IP address basis... any clues?

Thanks

Saludos, Juan.