On Ubuntu 12.04 i do have two psql one of those isn't working

I'm testing my second PostgreSQL install on Xunutu 12.04 after a disk crash.

Everything went well using command line where i was able, after config and
setup, to log into a db using :
$ psql <IPV4 or IPV6 of the server> -U yt -d yt_tests

Then i wanted to test postgres thru php where i got Http error 500.

After that i discovered that i do have TWO psql installed :

the first :
lrwxrwxrwx 1 root root 37 mars 6 2012 /usr/bin/psql ->
../share/postgresql-common/pg_wrapper

the second :
-rwxr-xr-x 1 root root 433224 août 17 00:58
/usr/lib/postgresql/9.1/bin/psql

the first is working not the second :

yt(at)D620 $ sudo -s -u postgres
[sudo] password for yt:
zsh: locking failed for */home/yt/*.zsh_history: permission non accordée:
reading anyway

using the first one :
postgres(at)D620 $ /usr/bin/psql
psql (9.1.5)
Type "help" for help.

postgres=# \q

using the second :
postgres(at)D620 $ /usr/lib/postgresql/9.1/bin/psql
psql: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
could not send startup packet: Relais brisé (pipe)
zsh: exit 2 /usr/lib/postgresql/9.1/bin/psql

then, i wonder how to workaround this "installation bugg" because i suspect
php is using the second not working psql where the first is the one being
in my PATH.
--
Yvon