I'm trying to use libusb-win32 (http://libusb-win32.sourceforge.net/)
via #libusb (http://www.icsharpcode.net/opensource/sharpusblib/) with
.NET 2.0 on Windows XP SP2.  I keep getting an exception from a
function, usb_get_busses().  It works the first time I call it, but
throws an exception if I call it after usb_get_busses():

Got Exception (Form1->parseBusses): System.AccessViolationException:
Attempted to read or write protected memory. This is often an indication
that other memory is corrupt.
  at USBlib.Internal.NativeMethods.usb_find_busses()

USBlib.Internal.NativeMethods contains the interop wrappers around the c
functions (code from #libusb):

[DllImport("libusb0.dll", CallingConvention = CallingConvention.Cdecl,
ExactSpelling = true), SuppressUnmanagedCodeSecurity]
public static extern int usb_find_busses();

[DllImport("libusb0.dll", CallingConvention = CallingConvention.Cdecl,
ExactSpelling = true), SuppressUnmanagedCodeSecurity]
public static extern usb_bus usb_get_busses();

The c function, usb_find_busses updates a global pointer, *usb_busses,
within the c code, and usb_get_busses() returns it (code from libusb-win32):

//usb.c

struct usb_bus *usb_busses = NULL;

int usb_find_busses(void)
{
 // updates the usb_busses pointer to point to a linked list of busses
}

struct usb_bus *usb_get_busses(void)  //returns the global pointer

Why is this crashing?  How do I fix it?  There should be no problm
calling usb_get_busses() as many times as desired.  Is this the wrong
way to deal with a return value of a pointer to a struct?

T