platform not supported

System.PlatformNotSupportedException was unhandled
  Message="PlatformNotSupportedException"
  StackTrace:
    at System.Text.Encoding.GetDataItem()
    at System.Text.CodePageEncoding..ctor()
    at System.Text.Encoding.GetEncoding()
    at System.Data.SqlClient.TdsParser.ProcessEnvChange()
    at System.Data.SqlClient.TdsParser.Run()
    at System.Data.SqlClient.TdsParser.Run()
    at System.Data.SqlClient.SqlInternalConnection.Login()
    at System.Data.SqlClient.SqlInternalConnection.OpenAndLogin()
    at System.Data.SqlClient.SqlInternalConnection..ctor()
    at System.Data.SqlClient.SqlConnection.Open()
    at DeviceApplication1.Form1.button1_Click()
    at System.Windows.Forms.Control.OnClick()
    at System.Windows.Forms.Button.OnClick()
    at System.Windows.Forms.ButtonBase.WnProc()
    at System.Windows.Forms.Control._InternalWnProc()
    at Microsoft.AGL.Forms.EVL.EnterMainLoop()
    at System.Windows.Forms.Application.Run()
    at DeviceApplication1.Program.Main()

SqlConnection conn = null;
 string conString;

conString ="Data Source=192.168.100.11;Initial Catalog=PDA;Integrated Security=SSPI;User ID=mydomain\\usewrid;Password=mypassword";

conn = new SqlConnection(conString);
conn.Open();