Problems with Postgresql upgrade

Hi,

I had PostgreSQL working nicely on my system, it was version 6.3.
I upgraded from RedHat linux 5.1 to 6.0. This happened to install
version 6.4 of postgres, now I can't get it to work.

I start the postmaster with the command:
su postgres -c "/usr/bin/postmaster -i -S -D /usr/db&"
And that seems to work.
But if I try to do anything like run psql, I get the error:

pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or
while processing
the request.

Has anyone any idea what can cause this?

--
// Michael Davis Happy Linux user and Solaris code slave
// http://www.interlog.com/~mbdavis
// From sunny Toronto