If anyone has any ideas about the problem outlined below, I'll be grateful.

I am running an old version (5) of Photoshop under Classic (OS 9.2.2) on a
new (I've had it about 6 weeks) G5 Mac, which boots into OS X (10.3.7).
This Photoshop came from an old Mac, and previously ran with no problems
under OS 8.6 on the old system. It is a legal copy that I was able to move
to the new machine with no apparent problems and I did not get any messages
complaining about anything. But since then it has been giving me a problem.

When I first transferred Photoshop to the new Mac it seemed to run OK. In
the last several weeks, however, I have been unable to use the Gaussian Blur
filter (which worked when I first put Photoshop on the new machine). The
little window with the slider that lets me adjust the filter and preview the
result interactively does not show up completely, and then I lose cursor
control. When I use Command+Option+Escape to bring up the "Force Quit
Applications" window, and force Photoshop to quit, it brings down Classic as
well. I have not gone through the complete set of Photoshop functions
systematically, but every other function I have tried works with no
problems.

Rebuilding the Classic desktop doesn't help. I tried deleting Photoshop and
reinstalling it on the new computer, but that didn't help either.

It almost seems like an extensions conflict, but I did not install any
Classic application. If there is one suspect, it is the program from which
this message is being posted: Outlook Express 5 [V 5.02 (2022)]. It was
already on the system when I got it, but I did not start using it right
away. I appear to have started using Outlook Express two days before I
reinstalled Photoshop, so that may be when I started having the problem with
Photoshop's Gaussian Blur filter.

However, I can't find any extension that seems to have anything to do with
Outlook Express, and as I said it was on the machine when I took it out of
the box. Also, I was using Outlook Express 5 (I was up to v 5.0.6, but
previously I had an older version) on the old Mac, with the same Photoshop,
with no conflicts. So the fact that the trouble started about the same time
I started using OE on the new Mac may be nothing more than a coincidence.

Sorry about the length of this post. I welcome any constructive
suggestions, especially from anybody who has seen a similar problem before.