C# Definition:

struct COPYDATASTRUCT {
    public int dwData;
    public int cbData;
    public IntPtr lpData;
}

VB Definition:

Structure COPYDATASTRUCT
   Public dwData As Int32
   Public cdData As Int32
   Public lpData As IntPtr
End Structure

User-Defined Field Types:

None.

Notes:

dwData defined in winuser.h as ULONG_PTR. I define it as (int) but probably it must be IntPtr

Define dwData and cbData all as IntPtr if you want them working on a 64-bit architecture !!!

struct COPYDATASTRUCT {
    public IntPtr dwData;
    public IntPtr cbData;
    public IntPtr lpData;
}