Scratch that. Just now I was able to see the following error in Emacs
without any shell buffer, while copying in Chome:

Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  dbus-handle-event((dbus-event (if above 1 2)))
  funcall-interactively(dbus-handle-event (dbus-event (if above 1 2)))
  command-execute(dbus-handle-event nil [(dbus-event (if above 1 2))] t)

On Sun, May 5, 2024 at 9:44 AM Kun Liu <kun.liu@gmail.com> wrote:

> I am not sure how VirtualBox deals with Ctrl-C on the Windows side. I
> will look into it when I have time.
>
> I did more tests. Observations:
>
> 1) It *appears* that the problem is there only when I have a shell buffer
> (M-x shell). I will do more tests and report back.
>
> 2) The error messages seem to vary. For example, I saw the following two
> different ones when copying:
>
> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
>   dbus-handle-event((dbus-event (calendar-cursor-holidays
> (calendar-current-date))))
>   funcall-interactively(dbus-handle-event (dbus-event
> (calendar-cursor-holidays (calendar-current-date))))
>   command-execute(dbus-handle-event nil [(dbus-event
> (calendar-cursor-holidays (calendar-current-date)))] t)
>
> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
>   dbus-handle-event((dbus-event (if above 1 2)))
>   funcall-interactively(dbus-handle-event (dbus-event (if above 1 2)))
>   command-execute(dbus-handle-event nil [(dbus-event (if above 1 2))] t)
>
> On Sun, May 5, 2024 at 9:12 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
>> > From: Kun Liu <kun.liu@gmail.com>
>> > Date: Sun, 5 May 2024 08:45:34 -0700
>> > Cc: 70760@debbugs.gnu.org
>> >
>> > I did (setq debug-on-error t), went to
>> https://en.wikipedia.org/wiki/Emacs, randomly selected a fragment
>> > "Emacs has over", then did a ctrll+c.
>> >
>> > Emacs in VirtualBox immediately showed the following:
>> >
>> > Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p
>> nil)
>> >   dbus-handle-event((dbus-event "[ \11]*$"))
>> >   funcall-interactively(dbus-handle-event (dbus-event "[ \11]*$"))
>> >   call-interactively(dbus-handle-event nil [(dbus-event "[ \11]*$")])
>> >   command-execute(dbus-handle-event nil [(dbus-event "[ \11]*$")] t)
>>
>> Does VirtualBox have anything in its documentation that suggests that
>> Ctrl-C on the Windows side will cause a D-Bus event on the VM side?
>>
>> Michael, any idea what is this D-Bus event, and what does it have to
>> do with copying into the Windows clipboard?
>>
>> Thanks.
>>
>