My setup has dual monitors. For a year, I have kept Outlook Express
(last version) open on the second monitor. Now, for some reason, when I
double click on an attachment, nothing happens. If I right click on the
attachment, the "Open" dialog appears on the primary monitor. I have
tried dragging everything to the second monitor, updating drivers, and
deactivating/activating the dual monitor setup. I am unable to get the
attachments to open with a double click.

If I move OE to the primary monitor, everything works as expected.
However, I much prefer to have OE in the second monitor. Any thoughts on
what I can do to fix or even troubleshoot the problem?