Postgres concurrency : urgent

Hi,

I'm having a postgres database accessed from perl using DBI and
DBD.

This application works fine when we are in single user. When we
go into multi-user, the app has concurrency problems.

The application has a sql query and updates onto the base table in
the sql query. We are using Select FOR UPDATE to open the
cursor and multiple update statements to update values on different
base tables. When multiple users are running the program, after a
few iterations postmaster startsputting out messages that there are
concurrency problems due to which the execute before the fetch
fails.
What I want to do is to wait for the other transactions updates to
get over and retry opening the cursor. This does not happen.
The moment I try to open the cursor again (using execute),
postmaster says that there is no connection !!

If I try and reconnecting again it starts giving pqreaddata() problems.
After sometime server crashes !!

We are using postgres 6.5.1, DBI-1.13, DBD 0.92

Please somebody help.

Thanks and regards,

Kimi