Some fixes for the last commit

src/slic3r/GUI/Plater.cpp

@@ -1941,6 +1941,7 @@ void Plater::priv::split_volume()
 
 void Plater::priv::schedule_background_process()
 {
+    delayed_error_message.clear();
     // Trigger the timer event after 0.5s
     this->background_process_timer.Start(500, wxTIMER_ONE_SHOT);
     // Notify the Canvas3D that something has changed, so it may invalidate some of the layer editing stuff.