Thank you anyone who has time to look at this problem with me. That is the message in the apache error log file that I can't seem to fix. After googling some, I have set:

and

The same error messages keep happening though. They seem to be happening less, and at least the website is working again. Before I turned those settings off, the website wouldn't display an entire page, images were messed up and not loading. It's a virtual CentOS 5.2 server running in ESX, with Apache 2.2.3, php 5.2.6, and mysql 5.0.45.

The IT guy where the server is, says he checked the logs for the cisco firewall and thinks their firewall is detecting a dos attack, whenever someone visits the website (?). It's the same firewall they've had for years, and we're talking about port 80 here.

Unrelated, but perhaps pertininent, what I did when they gave me this virtual server to install the website on was just that, install the website. But when it was time to go live I'm like, oh dangit, we gotta 7GB system drive thats full!! So he gave me 100 more virtual GBs to install, which I parted up into /var/log /var/www /var/database and /usr. I hope that isn't going to screw anything up, shouldn't, it's been running fine for a couple weeks. All this started this morning.

[Mon Sep 29 19:02:40 2008] [info] [client x.2.3.219] (104)Connection reset by peer: core_output_filter: writing data to the network
[Mon Sep 29 19:11:37 2008] [info] [client x.2.3.219] (104)Connection reset by peer: core_output_filter: writing data to the network

Googling for the error message gives mostly the same results: check the apache FAQ. Change the above settings. I've been through the first few pages of google results and am going deeper. If anyone has ideas they are welcomed and appreciated!

This problem is still happening. Unfortunately it is #1 on the Apache FAQ but the suggested workarounds do not work. It has to be a common everyday thing. Can this be happening because of the firewall? Is the firewall closing the connection to the client prematurely?

Lots of people asking this question on the internet but only the one answer provided anywhere, change EnableSendfile and EnableMMAP. Other people asking the question don't get responses and no one ever reports back to say what worked!

Come on linuxquestions.org, let's publish an answer to this and make it front and centre for anyone else who ever has this problem and searches google!

Unfortunately this is still happening and I have no idea why. Can anybody offer any clues?

[Fri Oct 03 12:10:16 2008] [info] [client x.128.157.245] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 12:17:38 2008] [info] [client x.45.83.97] (32)Broken pipe: core_output_filter: writing data to the network
[Fri Oct 03 12:49:21 2008] [info] [client x.244.164.61] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 12:51:54 2008] [info] [client x.244.164.61] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 12:52:13 2008] [info] [client x.7.128.34] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 14:37:06 2008] [info] [client x.244.32.28] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 14:47:26 2008] [info] [client x.161.51.2] (32)Broken pipe: core_output_filter: writing data to the network
[Fri Oct 03 15:09:02 2008] [info] [client x.159.247.120] (104)Connection reset by peer: core_output_filter: writing data to the network
[Fri Oct 03 15:46:09 2008] [info] [client x.128.49.182] (32)Broken pipe: core_output_filter: writing data to the network
[Fri Oct 03 18:07:53 2008] [info] [client x.55.110.29] (104)Connection reset by peer: core_output_filter: writing data to the network