pg_clog problem (PG version 7.4.5)

hackers,

I am having a problem with table (identified by pg_dump). I get the follow error when I try to COPY the table to
stdout (or /dev/null).

DB=# copy rnk to '/dev/null';
ERROR: could not access status of transaction 1076101119
DETAIL: could not open file "/usr/local/pgsql/data/pg_clog/0402": No such file or directory

Pg version is
select version();
version
-------------------------------------------------------------------------------------------------
PostgreSQL 7.4.5 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.3.4 (Debian 1:3.3.4-6sarge1)

I do have a good backup from the day before, if needed. is there a magic command to get me out of this?

Thanks
Jim