Removed and then missing pg_clog file

Hi,

We about a week ago installed a clean version of postgres
7.4.5 for testing purposes. For the last couple of days
for any transaction it has been complaining about: Thu Sep
23 09:36:24 2004: ERROR: could not access status of
transaction 941262
Thu Sep 23 10:10:01 2004: DETAIL: could not open file
"/nw/data/pgdata/pg_clog/0000": No such file or directory
Thu Sep 23 10:10:01 2004: ERROR: could not access status
of transaction 941355
Thu Sep 23 10:10:06 2004: DETAIL: could not open file
"/nw/data/pgdata/pg_clog/0000": No such file or directory

Now looking at the postgres logfile it also says (meaning
that it removed the log file thinking it was safe to
remove it):

Thu Sep 23 07:40:02 2004: LOG: removing file
"/nw/data/pgdata/pg_clog/0000"

What might be causing this error to occur?

Thanks..
Amin