problem with Access Violation, and I'm not sure where

[Matt via Digitalmars-d-learn]

I previously asked this over in the DigitalMars.D 
board(http://forum.dlang.org/thread/huftyrtbomaimuqkmkmy@forum.dlang.org#post-hrqvqlzzbkgafvjdtjnb:40forum.dlang.org), 
but it was suggested I ask it over here instead.

I have the following code and, despite trying to pinpoint it with 
try-catch blocks, I keep getting an Access Violation, and I'm 
really not sure where.

I'm using dub to build, but I've tried manually building as well, 
and I just get the same problem comes up.

The only module in the program is as follows (with the wrapper 
modules ripped out, so it's straight calls);

---

module app;

// own modules
import derelict.sdl2.sdl;

// standard library modules
import std.json;
import std.file;
import std.conv;
import std.stdio;
import std.datetime;

void main (string[] args){
	DerelictSDL2.load();
	if (!DerelictSDL2.isLoaded) assert(0, "DerelictSDL2 failed to 
load!");
	SDL_Init( SDL_INIT_EVERYTHING );
	
	scope(exit) SDL_Quit();
	
	SDL_Window* window;
	JSONValue cfg;
	
	try{
		cfg = loadConfig;
		
		auto width = to!int (cfg["window"]["width"].integer);
		auto height = to!int (cfg["window"]["height"].integer);
		
		window = SDL_CreateWindow (cfg["window"]["caption"].str.ptr, 
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, width, height, 
SDL_WINDOW_SHOWN);
	}
	catch(Error e){
		writeln ("error occurred before timing variable setup");
		return;
	}
	
	// set up timing variables
	auto duration = TickDuration (cfg["graphics"]["ticks"].integer);
	
	auto current_tick = Clock.currAppTick;
	auto target_tick = current_tick + duration;
	auto target_margin = target_tick + (duration/2);
	
	// main loop
	try{
		int* 	keys;
		ubyte*	numkeys;
		
		while (true){
			SDL_PumpEvents();
			numkeys = SDL_GetKeyboardState (keys);
			
			if (keys[SDL_SCANCODE_LALT] && keys[SDL_SCANCODE_F4]){
				SDL_DestroyWindow (window);
				break;
			}
			
			current_tick = Clock.currAppTick;
			if (current_tick >= target_tick){
				// this way, it will wait for the next frame, if there is 
less than half the time to the next frame left
				if (current_tick < target_margin){
					// update graphics and physics
				}
				// prep for next tick
				target_tick += duration;
				target_margin += duration;
			}
			
		}
	}
	catch(Error e){
		writeln ("error occurred during main loop");
	}
}

---

If anyone can help me with this, I would very much appreciate it.