Check if you have this enabled in radiusd.conf

        mschap {
                 with_ntdomain_hack = yes
        }

        realm ntdomain {
                format = prefix
                delimiter = "\\"
                ignore_default = no
                ignore_null = no
        }

and proxy.conf

        realm DEFAULT {
              strip
        }

If you only have one domain this will work. If you have different domains you'll need to setup the individual realms. Sounds like in your case you don't though.

Sergio Belkin wrote:

There are a few log entries like as as follows
 Auth: Login incorrect (rlm_ldap: User not found):
[QSARGENTINA\\amumenthaler] (from client UP-PVIII-VIII-Bis port 0 via
TLS tunnel)

Please could you help me to find a fix?