7.3.2 client connecting to 7.2.1 server problem

I have the following packages installed on my system:

libpq3: 7.3.2r1-5
python-pygresql: 7.3.2r1-5
postgresql: 7.2.1-2woody2
postgresql-client: 7.2.1-2woody2

In my application, which is written in python, I get a "server closed the
connection unexpectedly" exception after executing a few sql commands. I
print each query before I execute it (debugging) so I tried executing the
queries through psql with no problems.

Is there a known incompatibility between the versions of client/server that
I'm using? Or a known bug in pygresql?

I tried looking for an option to turn on query logging (I thought one was
present), but for some reason I didn't notice it. Is there a way to log
queries without restarting the server? It's a little troublesome for me to
start and stop the server (it's a production server), but I will if
necessary.

Here are the queries that execute (field names have been obfuscated):
BEGIN;
SELECT active FROM process WHERE xx='aa' FOR UPDATE;
UPDATE process SET active='t' WHERE xx='aa';
COMMIT;
-- server dies while trying to execute query below
SELECT bb.id as id,first,last,type from bb,cc where bb.id=bb_id order by dd
asc limit 1;

Sometimes, strangely, it makes it to a point further in the application but
crashes there instead one a different query (all the same program inputs).
I can't reproduce this result, although I recall it happening twice.

I've been using all that software together for quite some time with no
problems until now.

Any advice is appreciated.

Regards,
Jeff