Writes to transaction logs, Permission Denied

Hi

I am running:
Intel P4, 512Mb Memory, 20Gb Hard Drive
Windows2000 Pro, Service Pack 2
PostgreSQL 7.2.1-2
cygwin dll 1.3.12-2
ipc 1.11-1

The problem is, sometimes the server dies and when I look at the log,
this is what I get. (see below)

We have it running on two identical machines and both have the same
problem. Both were running without any problems up until a few weeks
ago.

We are running with fsync off, does this have anything to do with this?

Does PostgreSQL 7.2.1 have an issue with recyclying the transaction logs?
Could this problem be network related?
Should we upgrade cygwin and postgresql?

Thanks you

Colin

DEBUG: recycled transaction log file 0000000400000015
DEBUG: recycled transaction log file 0000000400000016
DEBUG: recycled transaction log file 0000000400000017
ERROR: cannot read block 0 of modem_pkey: Permission denied
NOTICE: Error occurred while executing PL/pgSQL function modem_updatesignalstrength
NOTICE: line 7 at SQL statement
ERROR: cannot read block 0 of modem_pkey: Permission denied
NOTICE: Error occurred while executing PL/pgSQL function modem_updatesignalstrength
NOTICE: line 7 at SQL statement
DEBUG: mdblindwrt: write() failed: Permission denied
ERROR: cannot write block 262 of 16557/16572 blind: Permission denied
NOTICE: Error occurred while executing PL/pgSQL function modem_updatesignalstrength
NOTICE: line 7 at SQL statement
ERROR: cannot extend messages: Permission denied.
Check free disk space.
FATAL 2: write of log file 4, segment 24, offset 12312576 failed: Permission denied
DEBUG: server process (pid 2324) exited with exit code 2
DEBUG: terminating any other active server processes
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend
died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am
going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.
DEBUG: all server processes terminated; reinitializing shared memory and semaphores
IpcMemoryCreate: shmget(key=5432001, size=2048000, 03600) failed: Not enough core

This error usually means that PostgreSQL's request for a shared
memory segment exceeded available memory or swap space.
To reduce the request size (currently 2048000 bytes), reduce
PostgreSQL's shared_buffers parameter (currently 100) and/or
its max_connections parameter (currently 50).

The PostgreSQL Administrator's Guide contains more information about
shared memory configuration.