I am trying to write a hello world type program for using virtual channels in the windows terminal services client.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }
    IntPtr mHandle = IntPtr.Zero;
    private void Form1_Load(object sender, EventArgs e)
    {
        mHandle = NativeMethods.WTSVirtualChannelOpen(IntPtr.Zero, -1, "TSCRED");
        if (mHandle == IntPtr.Zero)
        {
            throw new Win32Exception(Marshal.GetLastWin32Error());
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        uint bufferSize = 1024;
        StringBuilder buffer = new StringBuilder();
        uint bytesRead;
        NativeMethods.WTSVirtualChannelRead(mHandle, 0, buffer, bufferSize, out bytesRead);
        if (bytesRead == 0)
        {
            MessageBox.Show("Got no Data");
        }
        else
        {
            MessageBox.Show("Got data: " + buffer.ToString());
        }
    }

    protected override void Dispose(bool disposing)
    {
        if (mHandle != System.IntPtr.Zero)
        {
            NativeMethods.WTSVirtualChannelClose(mHandle);
        }
        base.Dispose(disposing);

    }
}

internal static class NativeMethods
{
    [DllImport("Wtsapi32.dll")]
    public static extern IntPtr WTSVirtualChannelOpen(IntPtr server,
        int sessionId, [MarshalAs(UnmanagedType.LPStr)] string virtualName);

    //[DllImport("Wtsapi32.dll", SetLastError = true)]
    //public static extern bool WTSVirtualChannelRead(IntPtr channelHandle, long timeout,
    //        byte[] buffer, int length, ref int bytesReaded);

    [DllImport("Wtsapi32.dll")]
    public static extern bool WTSVirtualChannelClose(IntPtr channelHandle);


    [DllImport("Wtsapi32.dll", EntryPoint = "WTSVirtualChannelRead")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool WTSVirtualChannelRead(
        [In()] System.IntPtr hChannelHandle
        , uint TimeOut
        , [Out()] [MarshalAs(UnmanagedType.LPStr)] 
          System.Text.StringBuilder Buffer
        , uint BufferSize
        , [Out()] out uint pBytesRead);

}

I am sending the data from the MSTSC COM object and ActiveX controll.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }

    private void Form1_Load(object sender, EventArgs e)
    {
        rdp.Server = "schamberlainvm";
        rdp.UserName = "TestAcct";
        IMsTscNonScriptable secured = (IMsTscNonScriptable)rdp.GetOcx();
        secured.ClearTextPassword = "asdf";
        rdp.CreateVirtualChannels("TSCRED");
        rdp.Connect();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        rdp.SendOnVirtualChannel("TSCRED", "Hello World!");
    }
}
//Designer code
// 
// rdp
// 
this.rdp.Enabled = true;
this.rdp.Location = new System.Drawing.Point(12, 12);
this.rdp.Name = "rdp";
this.rdp.OcxState = ((System.Windows.Forms.AxHost.State)(resources.GetObject("rdp.OcxState")));
this.rdp.Size = new System.Drawing.Size(1092, 580);
this.rdp.TabIndex = 0;

I am getting a execption every time NativeMethods.WTSVirtualChannelRead runs

Any help on this would be greatly appreciated.

EDIT -- mHandle has a non-zero value when the function runs. updated code to add that check.

EDIT2 -- I used the P/Invoke Interop Assistant and generated a new sigiture

    [DllImport("Wtsapi32.dll", EntryPoint = "WTSVirtualChannelRead")]
    [return: MarshalAs(UnmanagedType.Bool)]
    public static extern bool WTSVirtualChannelRead(
        [In()] System.IntPtr hChannelHandle
        , uint TimeOut
        , [Out()] [MarshalAs(UnmanagedType.LPStr)] 
          StringBuilder Buffer
        , uint BufferSize
        , [Out()] out uint pBytesRead);

it now receives the text string (Yea!) but it only gets the first letter of my test string(Boo!). Any ideas on what is going wrong?

EDIT 3 --- After the call that should of read the hello world;

BytesRead = 24

Buffer.Length = 1; Buffer.Capacity = 16; Buffer.m_StringValue = "H";