Postgres connection "Error status number -30105"

Hi all,
we are porting an application towards Postgres 8.4 on Ubuntu 12.04.

Today, we got the following error while running a form by a system user:

"Error status number -30105.
Could not connect to database."

The same form ran by another system user is working fine; the users have the same environment (a part from HOME, TTY and so on, of course).
Another strange fact is that the faulting user is able to connect using psql without any problem at all (like the working user, on the other hand)

We tried some debug with postgres server with the following results:

- Working user session:
2015-12-09 16:48:20 CET LOG:  00000: connection received: host=127.0.0.1 port=38235
2015-12-09 16:48:20 CET LOCATION:  BackendInitialize, postmaster.c:3280
2015-12-09 16:48:20 CET DEBUG:  00000: SSL connection from "(anonymous)"
2015-12-09 16:48:20 CET LOCATION:  open_server_SSL, be-secure.c:1007
2015-12-09 16:48:20 CET DEBUG:  00000: received password packet
2015-12-09 16:48:20 CET LOCATION:  recv_password_packet, auth.c:580
2015-12-09 16:48:20 CET LOG:  00000: connection authorized: user=<user> database=<database>
2015-12-09 16:48:20 CET LOCATION:  BackendInitialize, postmaster.c:3358

Faling user session:
2015-12-09 16:51:57 CET LOG:  00000: connection received: host=127.0.0.1 port=38239
2015-12-09 16:51:57 CET LOCATION:  BackendInitialize, postmaster.c:3280
2015-12-09 16:51:57 CET DEBUG:  00000: SSL connection from "(anonymous)"
2015-12-09 16:51:57 CET LOCATION:  open_server_SSL, be-secure.c:1007
2015-12-09 16:51:57 CET LOG:  08006: could not receive data from client: Connection reset by peer
2015-12-09 16:51:57 CET LOCATION:  pq_recvbuf, pqcomm.c:777


Any help appreciated, thanks anyone.

Regards,
Alessandro



------------------------------------------------------------------------------