Incomplete pg_dump operation

A shell script runs pg_dump once each day to backup a Postgresql database and then compress it for storage.  The script
andbackup process worked flawlessly for years, but now returns these error messages: 

   pg_dump: ERROR:  could not open relation with OID 2196359751
   pg_dump: SQL command to dump the contents of table "xyz" failed: PQendcopy() failed.
   pg_dump: Error message from server: ERROR:  could not open relation with OID 2196359751
   pg_dump: The command was: COPY public.xyz ({various_field_names}) TO stdout;

The pg_dump command halts with these error messages after copying or dumping about 50% of the database.  Accordingly,
onlya fraction of the database is actually being backed up.   

Is there corruption of some type inside my PostgreSQL database?  Has an index or something similar become corrupted?