[squid-users] Squid cannot start because it "can't open 'on' for writing..."

Hi,
     I'm having a strange problem with squid.
When I stop and restart the program, it fails to start; cache.log says
it can't open "on" for writing, and suggests to check that the parent
directory be writable by the user "squid".

I don't think this is a file permission issue, because even changing 777
permission to the entire /var/cache dir doesn't solve the problem.
I also tried lsof to check for locks on that file, but didn't find anything.

Yesterday I solved the problem by deleting the entire cache directory
and upgrading squid (now I'm running 2.6.STABLE4).

Googling around with strings from the message in the cache.log didn't
give much help, which makes me think I'm nearly the only one having this
issue.

The relevant lines from cache.log are:

--------- 8< ----------------
Squid Cache (Version 2.6.STABLE3): Terminated abnormally.
CPU Usage: 0.008 seconds = 0.008 user + 0.000 sys
Maximum Resident Size: 0 KB
Page faults with physical i/o: 0
2006/12/06 13:43:13| Starting Squid Cache version 2.6.STABLE3 for
i686-pc-linux-gnu...
2006/12/06 13:43:13| Process ID 15637
2006/12/06 13:43:13| With 1024 file descriptors available
2006/12/06 13:43:13| Using epoll for the IO loop
2006/12/06 13:43:13| Performing DNS Tests...
2006/12/06 13:43:13| Successful DNS name lookup tests...
2006/12/06 13:43:13| DNS Socket created at 0.0.0.0, port 33030, FD 5
2006/12/06 13:43:13| Adding nameserver 192.9.200.200 from /etc/resolv.conf
2006/12/06 13:43:13| Adding nameserver 151.99.125.1 from /etc/resolv.conf
2006/12/06 13:43:13| Adding nameserver 151.99.125.2 from /etc/resolv.conf
2006/12/06 13:43:13| Adding nameserver 151.99.125.3 from /etc/resolv.conf
2006/12/06 13:43:13| Adding nameserver 212.216.172.222 from /etc/resolv.conf
2006/12/06 13:43:13| Adding nameserver 212.216.112.112 from /etc/resolv.conf
FATAL: Cannot open 'on' for writing.
         The parent directory must be writeable by the
         user 'squid', which is the cache_effective_user
         set in squid.conf.
Squid Cache (Version 2.6.STABLE3): Terminated abnormally.
CPU Usage: 0.008 seconds = 0.008 user + 0.000 sys
Maximum Resident Size: 0 KB
Page faults with physical i/o: 0
------------- >8 ---------------

Thanks in advance.

-- 
Marcello Romani
Responsabile IT
Ottotecnica s.r.l.
http://www.ottotecnica.com