postgresql crushed with XLogWrite error

Hello dear list!
I am using postgresql 7.3.3 .Last night the errors occured.
Since then I can't start the postgresql !We are recovering from the type
by now ,but what happened?Is that a known bug?What to do next time?
The last change I made was that:
syslog=1
log_min_error_statement
log_timestamp = true
stats_reset_on_server_start = false
I can't think why those changes could crush the postgres!

Here is the log:

#============================================================================================
2004-01-05 05:30:35 PANIC: XLogWrite: write request 15/EF40E000 is past
end of log 15/EF40E000
2004-01-05 05:30:35 LOG: statement: update tyuta_rashum set chugid=521
where studentid=3587261 and maslulsignid=8014022 and c
ourseid=67538;
2004-01-05 05:30:35 LOG: server process (pid 2527) was terminated by
signal 6
2004-01-05 05:30:35 LOG: terminating any other active server processes
2004-01-05 05:30:35 LOG: all server processes terminated; reinitializing
shared memory and semaphores
2004-01-05 05:30:35 LOG: database system was interrupted at 2004-01-05
03:42:11 IST
2004-01-05 05:30:35 LOG: checkpoint record is at 15/EF40DFC0
2004-01-05 05:30:35 LOG: redo record is at 15/EF40DFC0; undo record is at
0/0; shutdown TRUE
2004-01-05 05:30:35 LOG: next transaction id: 88539506; next oid: 88761828
2004-01-05 05:30:35 LOG: database system was not properly shut down;
automatic recovery in progress
2004-01-05 05:30:35 FATAL: The database system is starting up
2004-01-05 05:30:35 FATAL: The database system is starting up
2004-01-05 05:30:35 FATAL: The database system is starting up
2004-01-05 05:30:35 LOG: ReadRecord: unexpected pageaddr 15/E640E000 in
log file 21, segment 239, offset 4251648
2004-01-05 05:30:35 LOG: redo is not required
2004-01-05 05:30:35 FATAL: The database system is starting up
2004-01-05 05:30:35 FATAL: The database system is starting up
2004-01-05 05:30:38 PANIC: XLogWrite: write request 15/EF40E000 is past
end of log 15/EF40E000
2004-01-05 05:30:38 LOG: startup process (pid 2529) was terminated by
signal 6
2004-01-05 05:30:38 LOG: aborting startup due to startup process failure
#============================================================================================

And since that, every time I am trying to start the db I get this:

#============================================================================================
2004-01-05 08:49:10 LOG: database system shutdown was interrupted at
2004-01-05 05:30:35 IST
2004-01-05 08:49:10 LOG: checkpoint record is at 15/EF40DFC0
2004-01-05 08:49:10 LOG: redo record is at 15/EF40DFC0; undo record is at
0/0; shutdown TRUE
2004-01-05 08:49:10 LOG: next transaction id: 88539506; next oid: 88761828
2004-01-05 08:49:10 LOG: database system was not properly shut down;
automatic recovery in progress
2004-01-05 08:49:10 LOG: ReadRecord: unexpected pageaddr 15/E640E000 in
log file 21, segment 239, offset 4251648
2004-01-05 08:49:10 LOG: redo is not required
2004-01-05 08:49:12 PANIC: XLogWrite: write request 15/EF40E000 is past
end of log 15/EF40E000
2004-01-05 08:49:12 LOG: startup process (pid 2907) was terminated by
signal 6
2004-01-05 08:49:12 LOG: aborting startup due to startup process failure
#============================================================================================

Here is the ls -al from the pg_clog directory.
I can't see any problems in log file 21:

-rw------- 1 postgres postgres 262144 Jul 6 2003 0000
-rw------- 1 postgres postgres 262144 Jul 10 02:10 0001
-rw------- 1 postgres postgres 262144 Jul 16 00:24 0002
-rw------- 1 postgres postgres 262144 Jul 21 21:15 0003
-rw------- 1 postgres postgres 262144 Jul 27 11:53 0004
-rw------- 1 postgres postgres 262144 Jul 29 11:11 0005
-rw------- 1 postgres postgres 262144 Jul 30 18:41 0006
-rw------- 1 postgres postgres 262144 Aug 3 20:24 0007
-rw------- 1 postgres postgres 262144 Aug 5 02:07 0008
-rw------- 1 postgres postgres 262144 Aug 6 18:52 0009
-rw------- 1 postgres postgres 262144 Aug 11 17:51 000A
-rw------- 1 postgres postgres 262144 Aug 12 18:50 000B
-rw------- 1 postgres postgres 262144 Aug 14 02:34 000C
-rw------- 1 postgres postgres 262144 Aug 15 13:40 000D
-rw------- 1 postgres postgres 262144 Aug 17 18:04 000E
-rw------- 1 postgres postgres 262144 Aug 20 15:58 000F
-rw------- 1 postgres postgres 262144 Aug 24 10:09 0010
-rw------- 1 postgres postgres 262144 Aug 25 14:52 0011
-rw------- 1 postgres postgres 262144 Aug 27 15:15 0012
-rw------- 1 postgres postgres 262144 Aug 31 14:58 0013
-rw------- 1 postgres postgres 262144 Sep 8 10:05 0014
-rw------- 1 postgres postgres 262144 Sep 8 13:55 0015
-rw------- 1 postgres postgres 262144 Sep 8 23:46 0016
-rw------- 1 postgres postgres 262144 Sep 9 21:01 0017
-rw------- 1 postgres postgres 262144 Sep 10 02:00 0018
-rw------- 1 postgres postgres 262144 Sep 10 09:49 0019
-rw------- 1 postgres postgres 262144 Sep 10 12:16 001A
-rw------- 1 postgres postgres 262144 Sep 10 16:28 001B
-rw------- 1 postgres postgres 262144 Sep 11 04:51 001C
-rw------- 1 postgres postgres 262144 Sep 11 14:00 001D
-rw------- 1 postgres postgres 262144 Sep 14 13:57 001E
-rw------- 1 postgres postgres 262144 Sep 15 02:02 001F
-rw------- 1 postgres postgres 262144 Sep 15 10:41 0020
-rw------- 1 postgres postgres 262144 Sep 15 12:37 0021
-rw------- 1 postgres postgres 262144 Sep 15 15:19 0022
-rw------- 1 postgres postgres 262144 Sep 15 22:58 0023
-rw------- 1 postgres postgres 262144 Sep 16 13:26 0024
-rw------- 1 postgres postgres 262144 Sep 17 06:43 0025
-rw------- 1 postgres postgres 262144 Sep 17 15:27 0026
-rw------- 1 postgres postgres 262144 Sep 18 13:14 0027
-rw------- 1 postgres postgres 262144 Sep 21 13:37 0028
-rw------- 1 postgres postgres 262144 Sep 22 09:21 0029
-rw------- 1 postgres postgres 262144 Sep 22 15:44 002A
-rw------- 1 postgres postgres 262144 Sep 23 01:15 002B
-rw------- 1 postgres postgres 262144 Sep 23 10:49 002C
-rw------- 1 postgres postgres 262144 Sep 23 14:36 002D
-rw------- 1 postgres postgres 262144 Sep 24 00:32 002E
-rw------- 1 postgres postgres 262144 Sep 24 11:56 002F
-rw------- 1 postgres postgres 262144 Sep 24 22:18 0030
-rw------- 1 postgres postgres 262144 Sep 25 14:11 0031
-rw------- 1 postgres postgres 262144 Sep 29 12:43 0032
-rw------- 1 postgres postgres 262144 Sep 30 00:31 0033
-rw------- 1 postgres postgres 262144 Sep 30 18:49 0034
-rw------- 1 postgres postgres 262144 Oct 2 14:04 0035
-rw------- 1 postgres postgres 262144 Oct 19 08:42 0036
-rw------- 1 postgres postgres 262144 Oct 19 12:59 0037
-rw------- 1 postgres postgres 262144 Oct 19 16:11 0038
-rw------- 1 postgres postgres 262144 Oct 20 10:18 0039
-rw------- 1 postgres postgres 262144 Oct 20 14:40 003A
-rw------- 1 postgres postgres 262144 Oct 21 09:03 003B
-rw------- 1 postgres postgres 262144 Oct 21 15:06 003C
-rw------- 1 postgres postgres 262144 Oct 22 11:47 003D
-rw------- 1 postgres postgres 262144 Oct 22 23:09 003E
-rw------- 1 postgres postgres 262144 Oct 23 16:15 003F
-rw------- 1 postgres postgres 262144 Oct 26 11:09 0040
-rw------- 1 postgres postgres 262144 Oct 26 15:16 0041
-rw------- 1 postgres postgres 262144 Oct 27 11:00 0042
-rw------- 1 postgres postgres 262144 Oct 27 15:42 0043
-rw------- 1 postgres postgres 262144 Oct 28 10:45 0044
-rw------- 1 postgres postgres 262144 Oct 28 19:55 0045
-rw------- 1 postgres postgres 262144 Oct 29 13:31 0046
-rw------- 1 postgres postgres 262144 Oct 30 11:04 0047
-rw------- 1 postgres postgres 262144 Oct 31 15:34 0048
-rw------- 1 postgres postgres 262144 Nov 2 15:27 0049
-rw------- 1 postgres postgres 262144 Nov 3 16:16 004A
-rw------- 1 postgres postgres 262144 Nov 4 18:06 004B
-rw------- 1 postgres postgres 262144 Nov 6 08:59 004C
-rw------- 1 postgres postgres 262144 Nov 9 10:24 004D
-rw------- 1 postgres postgres 262144 Nov 10 12:55 004E
-rw------- 1 postgres postgres 262144 Nov 11 16:06 004F
-rw------- 1 postgres postgres 262144 Nov 12 19:03 0050
-rw------- 1 postgres postgres 262144 Nov 13 15:45 0051
-rw------- 1 postgres postgres 262144 Nov 20 12:14 0052
-rw------- 1 postgres postgres 262144 Dec 17 19:56 0053
-rw------- 1 postgres postgres 122880 Jan 5 00:08 0054