pg 7.3 crash

Hi ,
I am running pg 7.3 on redhat 7.3.

If I send more complex request that take more time
the pg chrsh with this message:

WARNING:  Message from PostgreSQL backend:
        The Postmaster has informed me that some other backend
        died abnormally and possibly corrupted shared memory.
        I have rolled back the current transaction and am
        going to terminate your database system connection and exit.
        Please reconnect to the database system and repeat your query.
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
connection to server was lost.

Is it normaly for pg to crash?
How can I setup the box/pg to prevent this crash.

regards.