C#.Net Listen Only and ReadByteArray

I have a NI GPIB-USB-HS adapter running the 488.2 3.1.2 drivers.
It runs a C app in listen-only mode and captures bus data strings well.
I'm trying to get the same functionality using C#.Net.

So far I have tried the following code snippet in VS2010 (.Net 4.0)
with the corresponding NI 488.2 and Common assemblies referenced by the project.

Here is a snippet...

Form...
  private Board board = null;
   
Form_Load...             
  try {
    board = new Board(0);                  // ibfind(GPIB0);
    board.Reset();                         // ibonl();
    board = new Board(0);                  // ibfind(GPIB0);                 
    board.ListenOnlyMode = true;           // ibconfig(GPIB0, IbcLON, 1)
    board.IOTimeout = Timeoutvalue.t300ms; // ibconfig(GPIB0, IbcTMO, T300ms)
  }
  catch {
  ...
  }

Form_Shown...
  while(running)
  {
    Application.DoEvents();
    try {
      data = board.ReadByteArray(256); // ibrd
      length = board.LastCount;        // Ibcnt
    }
    catch {   
    ...
    }
  }

With the NI GPIB-USB-HS adapter disconnected from any GPIB host or devices,
the ReadByteArray lands in the catch every 300ms per the timeout value as expected.

With the NI GPIB-USB-HS adapter connected to a GPIB host and devices with data flowing,
the ReadByteArray method ends up in the catch everytime still and the length is always 0.
                         
Polling in C (ibrd/Ibcnt) is the only way I have been able to get Listen-Only to work.
 
What needs to be done in .Net to make Listen-Only work?

Here is a list of the calls in C that I use for Listen-Only to work...
Setup...
  Bd = ibfindA("GPIB0");
  ibonl(Bd, 0); // Take board offline - loses handle
  Bd = ibfindA("GPIB0");
  ibconfig(Bd, IbcSAD, 0x00);
  ibconfig(Bd, IbcLON, 1);
  ibconfig(Bd, IbcTMO, T300ms);
Poll...
  ibrd(Bd, ReadBuffer, 256);
  length = Ibcnt();

Thanks,

Steve