Call to GetActiveWindow() doesn't work

[[Deleted]]

I am trying to pass messages between various windows. At first I was trying to use FindWindow() to obtain the handles of various windows, but my results always came up as 0. So I decided to try just getting the handle of the calling window through GetActiveWindow(). Again, the result is 0. Why is this not working? Script code posted below:

//+------------------------------------------------------------------+
//| SendWinMessage. mq4 |
//| Copyright © 2007, MetaQuotes Software Corp. |
//| https://www.metaquotes.net/ |
//+------------------------------------------------------------------+
#property copyright "Copyright © 2007, MetaQuotes Software Corp."
#property link "https://www.metaquotes.net/"
#include <WinUser32.mqh>
#import "WinUser32"
int GetActiveWindow();
#import


int errorcatch = 0;
//+------------------------------------------------------------------+
//| script program start function |
//+------------------------------------------------------------------+
int start()
{
//----
int result;
result = GetActiveWindow();
errorcatch = MessageBox("The result is: " + result);
//----
return(0);
}
//+------------------------------------------------------------------+

BW