Have not heard back from support yet obviously, but I figured out a solution without ScanMessage.

Try this example (should run fine):
Code:

---

 
#include <acknex.h>
#include <default.c>
#include <windows.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

function main()
{
	wait(1);
	
	HMENU menu=CreateMenu();
	HMENU hSubMenu=CreateMenu();
	InsertMenu(hSubMenu,0,MF_BYPOSITION|MF_STRING,1,"BEEP");
	InsertMenu(hSubMenu,1,MF_BYPOSITION|MF_STRING,2,"QUIT");
	InsertMenu(menu,0,MF_BYPOSITION|MF_STRING|MF_POPUP,hSubMenu,"File");
	
	SetWindowLong(hWnd,GWL_WNDPROC, WndProc); 
	
	//Change Window style to activate Maximize button
	SetWindowLong(hWnd,GWL_STYLE, WS_CAPTION+WS_SYSMENU+WS_MINIMIZEBOX+WS_MAXIMIZEBOX+WS_SIZEBOX); 
	SetMenu(hWnd,menu);
	ShowWindow(hWnd,SW_SHOW);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){
	switch(message){
		case WM_LBUTTONDOWN:
			MessageBox(NULL, "L mouse down","info", MB_OK);
			break;
		case WM_RBUTTONDOWN:
			MessageBox(NULL, "R mouse down","info", MB_OK);
			break;
		case WM_COMMAND:
			switch(wParam){
				case 1: beep(); break;
				case 2: sys_exit(NULL);
			}
		default:
			return DefWindowProc(hWnd, message, wParam, lParam);
	}
	return(0);
}
 

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I will make a nice example with some common dialogs and post in Lite-C contributions