login problem

I am having a login problem using pgsql and php. It seems to be
either an authentication problem or a php problem.
I last was able to access my admin pages on the website in June of'
'05. Now I cannot access them even though the user/password
combinations are correct, the db appears to be ok as do all the php
files. I have compared the files from the website with the backups on
the local server and they appear ok.
I can write to the web db.
One strange entry in a php file for the db - there are two entries
for 2 different users and 2 different passwords. This is the same on
the website and on the backup; this has not changed since the login
was functional back in June.
It would appear that something has changed on the server - either the
postgresql version or the php version... I cannot imagine what else
could be the cause.
Any suggestions how to debug this thing?
Thanks in advance,
Philip