If you post an event in a response window that closes the response window, and call posted events in the Open event for a main window that displays when the response window is closed, the posted events in the Open event are not executed.
This is due to a limitation of the threading model in Web Forms applications.
To make sure that the posted events of the main window are executed, close the response window directly in a triggered event rather than in a posted event. Alternatively, move the code from posted events in the main window to events that are triggered directly by the user.