Another same issue on "NullReferenceException" :-
I have an (exe) executable program created in VB.NET 2003 that calls to a
MFC DLL written in VC++.NET 2003. I always get an error msg
"NullReferenceException: Object Reference Not Set to an Instance of an
Object" when my exe calls the following codes:

in VB.NET

   Declare Function test Lib "C:\Cyob\IOComm\Debug\IOComm.dll" _
   (ByVal a As Long, ByRef b As String) As Integer

    Dim did As Integer
    Dim ret As Integer

    ret = test(PortHnd, did)     //ERROR: Object Reference Not Set to an
Instance of an Object

in VC++.NET

extern "C" int APIENTRY test(HANDLE a, LPSTR b)
{
    strcpy(b, "hello");         //ERROR: Object Reference Not Set to an
Instance of an Object
    return 99;
}

Why is this happening? Any idea in solving such matter?
Thanks in Advance

Michael.