D2 Win API Problem

[A Bothe]

Hello guys,
I got a problem with the following code. I can compile it successfully but when 
I want to start it, there is just this "object.AccessVialotion"!
Even GetLastError() returns 0.... so the problem cannot be found in  
wrong-written names...

Thanks in advance!

import std.loader, std.c.windows.windows;

int function(HWND hwnd,char* text,char* title, uint style) tfunc=null;

class Module
{
        private HXModule hm;
        public HXModule Handle() {return hm;}
        this(string name)
        {
                hm=ExeModule_Load(name);
        }
        
        Fun GetSymbol(Fun)(ref Fun func,string name)
        {
                return func=cast(Fun)ExeModule_GetSymbol(hm,name);
        }
}


void main(){
        Module m=new Module("user32.dll");
        m.GetSymbol(tfunc,"MessageBoxA");
        
        tfunc(null,cast(char*)"Test",cast(char*)"TestTitle",MB_OK);
}



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