"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