[El Sanchez]

Ivan_009, ок. В процедуре CurPageChanged2 перед InitializeSlideShow отключаете стиль, а после DeinitializeSlideShow включаете назад.

Код:

procedure CurPageChanged2(CurPageID: Integer);
begin
 If CurPageID=wpInstalling then
  begin
   SetWindowLong(WizardForm.Handle, (-20), GetWindowLong(WizardForm.Handle, (-20)) xor $2000000);
   InitializeSlideShow(WizardForm.Handle, 0, 100, scaleX(778), ScaleY(358), {#Animation}, {#Stretch});
   ...
   if CurPageID=wpFinished then
  begin
   ...
   DeinitializeSlideShow;
   SetWindowLong(WizardForm.Handle, (-20), GetWindowLong(WizardForm.Handle, (-20)) or $2000000);
   ...
end;