Help:System.Nul lReferenceExcep tion with unmanaged memcpy

[noe]

I have done a DLL in unmanaged code C++ and in that dll I have defined
a function that use memcpy.This dll run ok.I use that dll in a
aplication in C# managed code in Visual Studio .NET. I import the
functions defined in the dll using DllImport and I have verified that
when in my dll I use memcpy then I have one error
:"System.NullRe ferenceExceptio n", and I don't known what happen?and I
must use memcpy in my dll.
Below is the definition of function in my DLL "DllWin32":
-------------------------------------------------------
DllExport bool Conectar()
{

HANDLE hAndle_ndisprot ocol;
hAndle_ndisprot ocol = CreateFile("\\\ \.\\\\miprotoco ldriverNDIS",
GENERIC_READ|GE NERIC_WRITE,
FILE_SHARE_READ |FILE_SHARE_WRI TE,//share for reading and
writing
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_ NORMAL,
(HANDLE) INVALID_HANDLE_ VALUE);
dwErr = GetLastError();
//*************** ****
if (dwErr!=0)
{
FormatMessage(F ORMAT_MESSAGE_A LLOCATE_BUFFER
|FORMAT_MESSAGE _FROM_SYSTEM |FORMAT_MESSAGE _IGNORE_INSERTS ,
NULL,
dwErr,
MAKELANGID(LANG _NEUTRAL, SUBLANG_DEFAULT ),
(LPTSTR)&buff,
0,
NULL);
//Display the string
MessageBox(NULL ,(LPTSTR)buff," Device.Error de
CreateFile",MB_ ICONWARNING);
//Free the buffer
LocalFree(buff) ;
}
//*************** ****
//Bind the file handle to the driver
bl=DeviceIoCont rol(hAndle_ndis protocol,
IOCTL_NDISPROT_ BIND_WAIT,
NULL,
0,
NULL,
0,
&dwReturned,
NULL);
dwErr = GetLastError();
//*************** ****
if (dwErr!=0)
{
FormatMessage(F ORMAT_MESSAGE_A LLOCATE_BUFFER
|FORMAT_MESSAGE _FROM_SYSTEM |FORMAT_MESSAGE _IGNORE_INSERTS ,
NULL,
dwErr,
MAKELANGID(LANG _NEUTRAL, SUBLANG_DEFAULT ),
(LPTSTR)&buff,
0,
NULL);
//Display the string
MessageBox(NULL ,(LPTSTR)buff," Device. Error llamada
IOCTL_NDISPROT_ BIND_WAIT",MB_I CONWARNING);
//Free the buffer
LocalFree(buff) ;
}
//*************** ****
WCHAR *pwDeviceName;
CHAR Buf[1024];
PNDISPROT_QUERY _BINDING pQueryBinding;
pQueryBinding = (PNDISPROT_QUER Y_BINDING)Buf;

bl = DeviceIoControl (hAndle_ndispro tocol,
IOCTL_NDISPROT_ QUERY_BINDING,
pQueryBinding,s izeof(NDISPROT_ QUERY_BINDING),
Buf, 1024,
&dwReturned,
NULL);
dwErr = GetLastError();
//*************** ****
if (dwErr!=0)
{
FormatMessage(F ORMAT_MESSAGE_A LLOCATE_BUFFER
|FORMAT_MESSAGE _FROM_SYSTEM |FORMAT_MESSAGE _IGNORE_INSERTS ,
NULL,
dwErr,
MAKELANGID(LANG _NEUTRAL, SUBLANG_DEFAULT ),
(LPTSTR)&buff,
0,
NULL);
//Display the string
MessageBox(NULL ,(LPTSTR)buff," Device. Error llamada
IOCTL_NDISPROT_ QUERY_BINDING", MB_ICONWARNING) ;
//Free the buffer
LocalFree(buff) ;
}
//*************** ****
//Convierto el nombre del dispositivo en un string Unicode(caracte res
anchos de 16 bits)
pwDeviceName=(W CHAR*)malloc(pQ ueryBinding->DeviceNameLeng th);

memcpy(pwDevice Name,((PBYTE)pQ ueryBinding+pQu eryBinding->DeviceNameOffs et),pQueryBindi ng->DeviceNameLeng th);

return true;
}

---------------------------------------
My application in C# in Visual studio .NET:
------------------------------------
[STAThread]
static void Main()
{
bool ok;
Application.Run (new Form1());
ok=ApiWin32.Con ectar();//Here is the error
System.NullRefe renceException
if (ok)
{
ApiWin32.Messag eBox(0,"Funcion a","Ejemplo de invocación de
plataforma",0);
}
else
{
ApiWin32.Messag eBox(0,"No funciona","Ejem plo de invocación de
plataforma",0);
}

}
-------------------------------------

ApiWin32 is class that I have defined:
------------------------------------
public class ApiWin32
{
[DllImport("user 32.dll", CharSet=CharSet .Auto)]
public static extern int MessageBox ( int hWnd,
String lpText,
String lpCaption,
uint uType) ;

[DllImport("DllW in32.dll", CharSet=CharSet .Auto)]
public static extern bool Conectar () ;
//Constructor de la clase
public ApiWin32()
{

}
}
-----------------------------
Please help me, I don't Known what happen.