Win32 with D: Using RegisterClassExA instead of RegisterClass

[BeschBesch]

So, I wanted to try out D as a better alternative to C/C++ and
now I bump into some minor problems. Basically, it seems the
WinAPI is limited to D.
My problem: Using WNDCLASS and RegisterClass works out fine but
when I try the Ex-versions (RegisterClassExA/WNDCLASSEX) windows
returns a INVALID_PARAMETER error, though I did not change
anything besides adding "Ex".

Where is the mistake or is my approach totally wrong?

module winmain;

import core.runtime;
import std.conv;
import std.utf;
import core.sys.windows.windows;

public import myWindows.d; // for extended WinAPI stuff...still
empty

pragma(lib, "gdi32.lib");
pragma (lib,"user32.lib");

extern (Windows)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR
lpCmdLine, int nCmdShow)
{
      int result;

      try
      {
          Runtime.initialize();

          result = myWinMain(hInstance, hPrevInstance, lpCmdLine,
nCmdShow);

          Runtime.terminate();
      }
      catch (Throwable o)               // catch any uncaught exceptions
      {
         MsgBox(o.toString(),"Runtime error");
           result = 0;          // failed
      }

      return result;
}

int myWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR
lpCmdLine, int nCmdShow)
{

        HWND wnd;
        MSG msg;
        WNDCLASSEXA wce;

        wce.cbClsExtra = 0;
        wce.cbWndExtra = 0;
        wce.hbrBackground = cast(HBRUSH)GetStockObject(WHITE_BRUSH);
        wce.hCursor = LoadCursorA(null,IDC_ARROW);
        wce.hIcon = LoadIconA(null, IDI_APPLICATION);
        wce.hIconSm = LoadIconA(null, IDI_APPLICATION);
        wce.hInstance = hInstance;
        wce.lpszClassName = cast(char*)("VolumeControl_Main");
        wce.style = 0;
        wce.lpszMenuName = null;
        wce.lpfnWndProc = &WinProc;

        if (!RegisterClassExA(&wce))
        {
                MessageBoxA(null,cast(char*)"RegisterClass failed!",
cast(char*) "Init-Error",0);
                return 0;
        }

        wnd =
CreateWindowExA(0,wce.lpszClassName,"TestBox",WS_OVERLAPPEDWINDOW,
250,250,250,250,null,null,hInstance,null);

        ShowWindow(wnd, SW_SHOWNORMAL);
        UpdateWindow(wnd);

        while (GetMessageA(&msg,null,0,0))
        {
                TranslateMessage(&msg);
                DispatchMessageA(&msg);
        }

        return 0;
}

extern(Windows)
LRESULT WinProc(HWND wnd, UINT msg, WPARAM W, LPARAM L) nothrow
{
        switch (msg)
        {
                case WM_DESTROY:
                        PostQuitMessage(0);
                        return 0;
                default:
        }

        return DefWindowProcA(wnd, msg, W, L);
}