"could not read block 0... " error followed by "database does not exist"

Hi. I am running Postgres 8.2.7 on a Linux system for over
a year now with no problems.

Today one of the database users reported the following error:

psql: FATAL: could not read block 0 of relation 1664/0/1262: read
only 0 of 8192 bytes

I tried stopping and restarting the Postgres server for the database.
>From the logfile:

LOG: received smart shutdown request
LOG: autovacuum launcher shutting down
LOG: shutting down
LOG: database system is shut down
LOG: database system was shut down at 2010-02-12 17:15:37 PST
LOG: autovacuum launcher started
LOG: database system is ready to accept connections

But when I try to connect to the database, I get the error message:

FATAL: database "subptf" does not exist

I tried stopping/restarting the database several times. I also
killed all user connections to the database.

How do I fix this problem?

Thanks,
Janet