Ajax POST - HTTP Status 12031 Error?

I have a web application (Classic ASP and VB COM+) that makes Ajax (using
Microsoft.XMLHTTP) calls to ASP/COM+ that submits form data (ultimately to a
database) and then returns an HTML fragment and inserts it into a specific
<DIV> on a web page. This code has worked for three years without a hitch,
and in fact, worked flawlessly until two days ago.

One of my customers (with dozens of users from one institution) started
receiving error messages from my Javascript Ajax functions (one below) that
indicated a status code of 12031 (Internet connection reset error). They are
all using IE 6.0 with XP. Different users at that institution had the same
error, but to my knowledge none of my other customers or their users outside
that institution had any problems and I could not recreate the errors on my
machine accessing the web application (I only use one server for the entire
country). And then yesterday, there were no errors at all from that place
(it may have been a busier day the day before).

So, what exactly does this status code mean? Is this a client or server
problem? Is it a network problem? Mine or theirs? Does it have anything to
do with firewalls or security settings at the institution where the problems
occurred?

What can I do to track down or diagnose this issue and resolve it?

Thanks for any help or direction as I have no clue where even to start with
such nebulous error messages with code that seemed time-tested until two
days ago.


function onReadyStateChangeEventHandler() {
if (req.readyState == 4) {
if (req.status == 200) {
document.getElementById(targetDIV).innerHTML = req.responseTex
} else {
var strDetails;
strDetails = "There was a problem processing your " +
httpReqType + " request.\n\nDIV: " + targetDIV + "\nStatus Text: " +
req.statusText + "\nStatus Code: " + req.status;
alert(strDetails);
}
}
}