WM_QUERYENDSESS ION not caught on WinXP Pro SP2

[Mike S]

Hi all,

I'm trying to capture the WM_QUERYENDSESS ION message in a Windows Form
and prevent the session from shutting down. I overrode the Form's
WndProc method to do this, but I'm completely dumbfounded, because it
seems to work on every Windows computer I can find in the office and at
home (Win98 and WinXP machines), _except_ my development machine. On my
machine, the Form's WndProc method never even receives the
WM_QUERYENDSESS ION message, and so Windows shuts down. I'm running
Windows XP Professional Service Pack 2, and I'm guessing it might be
caused by a bug in SP2 or some small change to the shutdown protocol,
but I won't rule out other possibilities. In testing, I stripped
everything from the Form code except for the WndProc method and still
no dice. Here's the WndProc I'm using:

Protected Overrides Sub WndProc(ByRef m As
System.Windows. Forms.Message)

Select Case m.Msg
Case &H11 'WM_QUERYENDSES SION
MsgBox("WM_QUER YENDSESSION received")
'Stop the shutdown by returning 0
m.Result = IntPtr.Zero
Exit Sub
End Select

MyBase.WndProc( m)

End Sub

Microsoft docs say the WndProc method corresponds exactly to the WinAPI
WindowProc function, so I take that to mean that VB.NET will not filter
any messages before WndProc is called. I know the form's message pump
gets started, because in other tests I added code to the event handlers
and form events were raised without a hitch. I also know it's not a
VB.NET bug, because I wrote code to do the same thing in VB6 and it
also never receives the WM_QUERYENDSESS ION message on shutdown. I
thought it might be the case that another app gets the
WM_QUERYENDSESS ION and returns 0, and so my app never receives the
message, but that can't be it AFAIK, because the system always just
abruptly shuts down; my app never displays the message box on my
machine. And yes, I compiled the code and ran the actual EXE; I didn't
run the code from the IDE. I'm at a complete loss, because as I
mentioned, the code seems to work great on any computer except my own.

Even weirder: I just ran the code one more time on my machine, and it
worked...I didn't touch the source code at all, I just re-ran the EXE
that I had previously compiled and which wasn't working before.

Any other ideas as to what would prevent an app from receiving a
WM_QUERYENDSESS ION on system shutdown besides another app processing
the message first and returning 0?

--
Mike S