The backend has broken the connection...

I am running several databases on a PostgresQL server and webapps to go
with them on another server. For the past couple of days, several times
a day I've been getting a "The backend has broken the connection.
Possibly the action you have attempted has caused it to close." error.
When this happens, all connections close and anyone in the middle of a
session is screwed. They have to shut down their browsers and start
over. I'm keeping logs of almost all SQL queries executed, and there
seems to be no pattern to when this happens. I am running postmaster
with a buffer size of 1024 and a max backends of 256, but I am not
reaching the 256 limit. I doubt that I'm even getting to 100 concurrent
connections at a time.

my specs:
postgresql 7.1.3
java sdk 1.4 beta 1
apache 1.3.19
tomcat 4.0.1

I have a second web server on which I tried java sdk 1.4 beta 3 and the
most recent JDBC driver (which doesn't compile under Java 1.4, btw), and
I don't think it helped (although it's hard to tell because the two web
servers are accessing the same databases concurrently).

I can't use Java 1.3 because certain JSP pages crash the VM when
compiled.

Can anyone tell me why I keep getting this message and what I can do
about it?

Thanks
Ben
bcarterette(at)liberty(dot)k12(dot)mo(dot)us