[ADMIN] missing chunk number 0 for toast value

Our database seems to have been corrupted.  It is a heavily used database, and went several months without any type of vacuuming.  When we finally realized that it wasn't being vacuumed, we started the process, but the process never successfully completed, and our database has never been the same since. 

The exact error that we receive now is as follows:

postgres@server:~> pg_dumpall -p 5433 > dbmail_dumpall_23092008.sql
pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: missing chunk number 0 for toast value 554339
pg_dump: The command was: COPY public.dbmail_messageblks (messageblk_idnr, physmessage_id, blocksize, is_header, messageblk) TO stdout;
pg_dumpall: pg_dump failed on database "dbmail", exiting

We have tried using the -d option of the pg_dumpall so we could get a full dump of the database, and just start over from that, but that fails as well.  We have also tried reindexing the table, but although the reindex didn't fail, it didn't solve our problem either.  Our next option is to do a full vacuum, but we are reluctant to take our mail server down for that long, especially when we do not know for sure that it will either succeed or fix our problem.  I have searched the forums, but was unable to find a solution that we have not already tried.  The solutions didn't appear to help others who had this problem either. 

Any suggestions?

Thanks,
BJ