could not open relation with OID 2610

I'm no more able to connect to a database and the error is:

FATAL: could not open relation with OID 2610

The database was running inside a vmware virtual machine, the operating
system is Ubuntu server 8.04 and the postgresql version is 8.3.

I still can't figure out what happened more than a month ago and since
so long time passed we have no backups for it.

Since I can't connect to the database I can't reindex the system tables.
I just tried to connect to the database with the --single and -P options
but without success.

There is anything I can do to try to fix it?

Thanks,

maja