FATAL 2: open of /usr/local/pgsql/data/pg_clog/0943 failed

I have this error in postgres log
FATAL 2:  open of /usr/local/pgsql/data/pg_clog/0943 failed: No such file or
directory
When it happend i did indexing on big table (~32M rows)
On small selects, inserts, updates all seems to work fine, but when I try to
do select count(*) from big table or intex it, then server crashes and
automaticaly restarts (file name in error message changes from time to time)
Theare is about 3.5GB free disk space.
Postgres version 7.2.1
Theare is no more unusual messages in log.

What happend?
How to fix this problem?
Google didn't help so much :(

Mark
P.S.
Additional info:
last files in /usr/local/pgsql/data/pg_clog are
-rw-------    1 postgres daemon     262144 Jan 31 16:17 0099
-rw-------    1 postgres daemon     262144 Feb  3 09:11 009A
-rw-------    1 postgres daemon     262144 Feb  3 16:26 009B
-rw-------    1 postgres daemon     262144 Feb  4 13:54 009C
-rw-------    1 postgres daemon     262144 Feb  5 11:11 009D
-rw-------    1 postgres daemon     262144 Feb  5 21:32 009E
-rw-------    1 postgres daemon     262144 Feb  7 10:52 009F
-rw-------    1 postgres daemon     262144 Feb  7 14:35 00A0
-rw-------    1 postgres daemon     262144 Feb  9 21:57 00A1
-rw-------    1 postgres daemon     262144 Feb 10 16:29 00A2
-rw-------    1 postgres daemon     262144 Feb 11 13:06 00A3
-rw-------    1 postgres daemon     262144 Feb 11 23:22 00A4
-rw-------    1 postgres daemon     262144 Feb 12 15:53 00A5
-rw-------    1 postgres daemon     262144 Feb 13 13:52 00A6
-rw-------    1 postgres daemon     262144 Feb 14 10:33 00A7
-rw-------    1 postgres daemon     262144 Feb 15 13:27 00A8
-rw-------    1 postgres daemon     262144 Feb 17 12:44 00A9
-rw-------    1 postgres daemon     237568 Feb 17 20:44 00AA
That's all