pg_connect sometimes works sometimes not

["pobox@xxxxxxxxxxxxx" <pobox@xxxxxxxxxxxxx>]

Hello,

we migrated a php code from FreeBSD 5.x, PostgreSQL 8.x and php 4.x - to 
the latest versions of these, keeping the configuration options. Now 
pg_connect started to fail on irregular intervals for no obvious reason. 
Before we had a problem with the number of connections, but we monitored 
them and they are less than 10 (out of 100 available).

What other variable (which are sometimes there, sometimes not) reasons 
there can be pg_connect to fail?

Thank you,
Iv