could not open file "pg_clog/0BFF"

Hi,

While checking the logfiles of our postgresql server I noticed the error
mentioned in the subject:

ERROR: could not access status of transaction 3221180546
DETAIL: could not open file "pg_clog/0BFF": No such file or directory

Searching on google told me that this could be solved by creating the file
mentioned in the error using /dev/zero as input.

After I have done that and taking another look at the login I also noticed
that this error started to show up in the loggin since the 1st of August
and from the same date the autovacuum was only vacuuming the 'template0'
database.

Right now I have created the "pg_clog/0BFF" file and manually started a
vacuum.

And now my questions:

Are those mentioned steps the appropriate steps or should we do anything
else?

What could have caused the error "could not access status of transaction
3221180546" and is it more than just coincidence that since that moment
the vacuum stopped running?

Is there anything we can do to prevent this in future use?

Besides we are using PostgreSQL 8.1.3.

Any help would be appreciated.

Regards,
Patrick Lindeman