The Delphi Bug List

It is a conflict with the Microsoft Identity Manager (msident.dll), used by MS Outlook Express and possibly other MS apps. The Identity Manager calls SetProp to set a window property on the desktop window (GetDesktopWindow) with a value of $00098053. Unfortunately, this property sometimes has the same atom ID as the atom used internally by the VCL when accessing its own properties. When that happens and the VCL calls FindControl with the desktop window handle, it will get back the value set by the Identity Manager - $00098053. Since that is not a valid pointer, an access violation occurs.

For more details, see the thread on Google Groups.

Delphi 6

function FindControl(Handle: HWnd): TWinControl;
var
  PID: DWORD;
begin
  Result := nil;
  if (Handle <> 0) then
  begin
    if (GetWindowThreadProcessId(Handle, @PID) <> 0) and
       (PID = GetCurrentProcessId) then
    begin
      if GlobalFindAtom(PChar(ControlAtomString)) = ControlAtom then
        Result := Pointer(GetProp(Handle, MakeIntAtom(ControlAtom)))
      else
        Result := ObjectFromHWnd(Handle);
    end;
  end;
end;

...

function IsDelphiHandle(Handle: HWND): Boolean;
var
  PID: DWORD;
begin
  Result := False;
  if Handle <> 0 then
  begin
    if (GetWindowThreadProcessId(Handle, @PID) <> 0) and
       (PID = GetCurrentProcessId) then
    begin
      if GlobalFindAtom(PChar(WindowAtomString)) = WindowAtom then
        Result := GetProp(Handle, MakeIntAtom(WindowAtom)) <> 0
      else
        Result := ObjectFromHWnd(Handle) <> nil;
    end;
  end;
end;

function FindControl(Handle: HWnd): TWinControl;
var
  PID: DWORD;
begin
  Result := nil;
  if Handle <> 0 then
  begin
    if (GetWindowThreadProcessId(Handle, @PID) <> 0) and
       (PID = GetCurrentProcessId) then
      Result := Pointer(GetProp(Handle, MakeIntAtom(ControlAtom)));
  end;
end;

...
 
function IsDelphiHandle(Handle: HWND): Boolean;
var
  PID: DWORD;
begin
  Result := (Handle <> 0) and
    (GetWindowThreadProcessId(Handle, @PID) <> 0) and
    (PID = GetCurrentProcessId) and
    (GetProp(Handle, MakeIntAtom(WindowAtom)) <> 0);
end;