C sharp - Error extraño

Hola, estoy tratando de conectar postgres con c# y hice el siguiente programa para testear la conexion pero me da un error que no se que es cuando presiono el boton. el codigo es como sigue:

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using Npgsql;

namespace WindowsApplication1
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Button button1;
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components = null;

public Form1()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();

//
// TODO: Add any constructor code after InitializeComponent call
//
}

/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(72, 8);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(112, 24);
this.button1.TabIndex = 0;
this.button1.Text = "button1";
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(292, 266);
this.Controls.AddRange(new System.Windows.Forms.Control[] {
this.button1});
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);

}
#endregion

/// <summary>
/// The main entry point for the application.
/// </summary>
public static void Main()
{
Application.Run(new Form1());
}

private void button1_Click(object sender, System.EventArgs e)
{
try
{
string connectionString =
"Server=localhost;" +
"Database=prueba;" +
"User ID=postgres;" +
"Password=ninguna;";
IDbConnection dbcon;
dbcon = new NpgsqlConnection(connectionString);
dbcon.Open();
dbcon.Close();
dbcon = null;
}
catch
{
MessageBox.Show("Se capturo un error.");
}

}
}
}

y el mensaje de error es:

An unhandled exception of type 'System.IO.FileNotFoundException' occurred in system.windows.forms.dll

Additional information: File or assembly name System, or one of its dependencies, was not found.

Les agradeceria me digan que ocurre y si es posible como solucionarlo.
Gracias.
Saludos.

Carlos

checa si tienes referenciado System en tu refererencias del projecto

Hola, ya resolvi el problema, no tiene nada que ver con el codigo ni ocn las referencias, el IDE del VC 2002(frameowrk 1) genera conflicto no se porque y me da ese error. Instale el # Develop y el mismo codigo funciona sin problemas.
Gracias por la ayuda de todas maneras.

Carlos