getInherits(): SELECT failed.

I have inherited a database apparently set up using postgres7.0.2.  I
now want to dump the database in preparation for tidying up and
upgrading to the current version of postgresql.  However, pg_dumpall
gives:

pg_dumpall >db.out
getInherits(): SELECT failed.  Explanation from backend: 'ERROR:
Attribute 'inhrel' not found
'.

A previous message in this list proposed that this error was generated
when a version 6 database is dumped using version 7 software.  I think
this is unlikely to be the explanation here (for example, psql 7.0.2
reads the database without complaint), but it is a possibility.  My
questions for the list:

1. How do I find the version numbers of (a) the database and (b) the
pg_dump code, given that I am not certain about their past history.

2.  More importantly, how do I work around the error, so that I can dump
the database and move up to version 7.1?

Cheers,

Nigel