C#

/// <summary>
/// Structure for storing a reading and additional data for that reading.
/// </summary>
[StructLayout(LayoutKind.Sequential, Pack = 1)]
internal struct Reading
{
    public float value;
    public reading_info_struct info;

    /// <summary>
    /// Converts reading data to a string.
    /// </summary>
    /// <returns>Reading converted to string.</returns>
    public override string ToString() {
        return value.ToString();
    }

    #region Byte conversions

    public unsafe byte[] ToBytes() {
        byte[] arr = new byte[sizeof(Reading)];
        fixed (byte* parr = arr) {
            *((Reading*)parr) = this;
        }
        return arr;
    }

    public static unsafe Reading FromBytes(byte[] arr) {
        if (arr.Length < sizeof(Reading))
            throw new ArgumentException();

        Reading s;
        fixed (byte* parr = arr) {
            s = *((Reading*)parr);
        }
        return s;
    }

    #endregion
}

<br />
// C# class<br />
class MyDotNetClass<br />
{<br />
 String AnyMethod( Microsoft.Office.Interop.Excel.Range aRange )<br />
 {<br />
        object[,] formula = (object[,])aRange.FormulaR1C1;<br />
        // I can get the formulas like CONCATENATE( A1,B1 ) or<br />
        // references like D14<br />
<br />
        // most of methods and properties thrown an exception<br />
<br />
        // I cannot even get the Value or call get_Value<br />
        // I ahve this excepion<br />
        // "Old format or invalid type library. (Exception from HRESULT: <br />
        //  0x80028018 (TYPE_E_INVDATAREAD)) System.SystemException<br />
        //  {System.Runtime.InteropServices.COMException}<br />
<br />
 }<br />
}<br />
<br />
'VB CODE<br />
Function MyFoo( aRange As Range) As String<br />
Dim myLibObj As New MyLib<br />
MyFoo = myLibObj.AnyMethod( aRange )<br />
End Function<br />

namespace WindowsFormsApplication1
{
  public partial class Form3 : Form
  {
    Form4 f4 = null;

    public Form3()
    {
      InitializeComponent();
      this.IsMdiContainer = true;
      f4 = new Form4();
      f4.MdiParent = this;      
      f4.Show();

      // Current directory here points to the debug folder
      string ctDir = System.Environment.CurrentDirectory;
      
    }

    private void openToolStripMenuItem_Click(object sender, EventArgs e)
    {
      if (DialogResult.OK == openFileDialog1.ShowDialog())
      {
        f4.OpenFile(openFileDialog1.FileName, this);        
      }

      // Current directory here points to the directory which you opened file from open dialog 
      string ctDir = System.Environment.CurrentDirectory;
      MessageBox.Show(ctDir);
    }
  }
}

public partial class Form4 : Form
  {
    public Form4()
    {
      InitializeComponent();      
    }

    
    public void OpenFile(string filename,Form  parent)
    {
      richTextBox1.LoadFile(filename);
    }
  }