"expected authentication request from server, but received..."

Hello,

I have a very old postgres 6.4 installation. I'm trying to connect to it
from a fresh, up-to-date Debian-host, but I'm constantly getting (from DBI
and PHP as well) this error message:

# ./update_dns.pl
DBI connect('dbname=dns;host=sql;authtype=password','dns',...) failed:
expected authentication request from server, but received U
at ./update_dns.pl line 237

Connection with psql works OK. Connecting from different (older) hosts
with DBI/PHP works perfect as well. Something must have changed in recent
versions of libpq and now it doesn't work. I looked into source code and
found that the server's message at the very start of conversation appears
to be something else than the libpq expects. But how to fix it?! Has the
protocol change or what?

P.S. Don't tell me to upgrade postgres :) It must stay like that for some
reasons which are beyond me.
--
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