NamedPipe between Windows Form and background worker fails

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C++/CLI

BackgroundWorker

This is my first post here and I'm brand new to .NET. I'm creating a Windows Forms application using C++/CLI that needs to have bidirectional communication with several worker threads. I read the tutorials on the background threads and created a simple Form with a TextBox that starts several background workers (bw's). Each of the bw runs a do-forever loop that occasionally sends a data structure to the Form using bw->ReportProgress(0, my_data_structure), and the Form's ProgressChanged() event formats the data into a string that it Appends to the TextBox.

All this was working well but I needed a way for the Form to send data to the bw's. Named Pipes seemed to be a reasonable way to do this, but i can't get it to work.

In Form1.h, I added private variables:

private:
    System::IO::Pipes::NamedPipeServerStream ^pipeServer;
    array<byte> ^msgOut;

Then in Form1 c'tor:

        Form1(void)
        {
            InitializeComponent();
            // create named pipe to each subsystem
            this->msgOut = (gcnew array<byte>(256));
            this->pipeServer = (gcnew NamedPipeServerStream("pipeStream1", PipeDirection::Out));

            // start each subsystem (background worker) thread
           this->Arm1Thd->RunWorkerAsync();
        }
and
    private:
        System::Void ProgressChanged(System::Object^  sender, System::ComponentModel::ProgressChangedEventArgs^  e) {
            //this value can be anything, not used here 
            int Value = e->ProgressPercentage;
            this->pipeServer->WaitForConnection();    // not sure this is needed
            this->pipeServer->Write(msgOut, 0, msgOut->GetLength(0));
            ...
        }

In the background worker thread:

void Form1::TestCycle( BackgroundWorker^ bw, int SubSysID )
{
    array<byte> ^inMsg = (gcnew array<byte>(256));
    unsigned    msg_cnt = 0;
    int            len;

    System::IO::Pipes::NamedPipeClientStream  ^pipeClient =
        gcnew NamedPipeClientStream(".", "pipeStream1", PipeDirection::In);
    pipeClient->Connect();        // block until connected
    bw->ReportProgress(0, msg_cnt++);

    while (!bw->CancellationPending)
    {
        len = pipeClient->Read(inMsg, 0, inMsg->GetLength(0));
        ....
        System::Threading::Thread::Sleep(2000);           // set breakpoint here
        bw->ReportProgress(0, msg_cnt++);
    }
}

So the order of execution is:

1) Form1 loads, creates the NamedPipe, starts the background worker TestCycle
2) TestCycle sends a ProgressReport then blocks on NamedPipe Read()
3) Form1::ProgressChanged() gets the report, writes it to TextBox then Writes to NamedPipe.
4) TestCycle NamedPipe Read() returns, so he sleeps awhile then goes to step 2.

The first ProgressReport from TestCycle startup code shows up in Form1::TextBox.
Then the first pipeClient->Read completes, and the second ProgressReport is displayed.
But just after that, I get:

An unhandled exception of type 'System.Reflection.TargetInvocationException' occurred in mscorlib.dll

Additional information: Exception has been thrown by the target of an invocation.

Can anyone tell me what's going wrong, or even how to find what's going wrong?