select failure

Ideas where I should look for the answer to this problem & how I should fix
it?

observer=# select host, current_route, count(current_route)
observer-# from messages_200205
observer-# group by host, current_route;
FATAL 2:  open of /var/lib/postgres/data/pg_clog/0534 failed: No such file
or directory
server closed the connection unexpectedly       This probably means the server terminated abnormally       before or
whileprocessing the request.
 
The connection to the server was lost. Attempting reset: NOTICE:  Message
from PostgreSQL backend:       The Postmaster has informed me that some other backend       died abnormally and
possiblycorrupted shared memory.       I have rolled back the current transaction and am       going to terminate your
databasesystem connection and exit.       Please reconnect to the database system and repeat your query.
 
Failed.

--
Ian Cass