This is a strange one.

We're a public school system with about 1500 computers. We're
experiencing this problem at only one of our 6 buildings, and it does
seem to be specific to the hardware OR configuration in that one building.

In preparation for the new school year we upgraded all PC's from Zen 4
to Zen 7. We replaced McAfee 7 and 8 with Sophos AV (current), managed.
We added a bunch of Windows Update patches, etc., onto the machines;
unfortunately I don't have a list of the specific patches and updates,
but it was on the order of 40 items.

Almost all of the computers in our high school building are experiencing
the same problem, a Windows Explorer error with NTDLL.DLL at startup,
followed by a Dr. Watson report. Windows Explorer will shut down and
restart, *sometimes* leaving the computer fully functional.

These are relatively old Windows XP SP2 Tangent computers with Nvidia
Vantage video cards, and Intel Pro 10/100 NICs. We have tried a variety
of driver updates with no change.

Here's what seems to fix it: The problem computers all have the old
Eudora beta 5.1 email client, advertising support. Those that do not
experience the problem have different versions of Eudora, all newer.
The Eudora 5.1 beta is several years old (maybe 4 years). [Note: I've
only been here 3 years, and the machines in this building have been the
responsibility of one of our PC technicians, not the network
administrator. In other words, I can't explain *WHY* we're running this
version of Eudora.]

My question is this: Given this set of factors, what might be the actual
CAUSE of the problem? Any ideas? It was obviously triggered by the
various changes we implemented leading into the new school year, but
which one? It didn't show in our testing, of course, largely because we
didn't test the email program that had been installed forever.