cosa sarebbe questo errore??

Exception Details: System.Data.OleDb.OleDbException: No value given for one or more required parameters.

Source Error:


Line 29: Dim objReader As oleDbDataReader
Line 30: Con.Open()
Line 31: objReader = myCommand.ExecuteReader()
Line 32: If Not objReader.Read() Then
Line 33: Response.Redirect("http://www.noidellac.it/compiti/default.aspx?error=1")

il codice della funzione è questo:
codice:
 Sub Login(sender As Object, e As System.EventArgs)
  Dim Con As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " _
  + "Data Source=c:\\hosting\\noidellac.it\\wwwroot\\mdb-database\\regarray.mdb")
  Dim sqlString = "SELECT * FROM utenti WHERE password ='" & txtPass.Text & "', username='" & txtId.Text & "'"
  Dim myCommand As New OleDbCommand(sqlString, Con) 
  Dim objReader As oleDbDataReader
  Con.Open()
  objReader = myCommand.ExecuteReader()
  If Not objReader.Read() Then
   Response.Redirect("http://www.noidellac.it/compiti/default.aspx?error=1")
  Else
   Session.Item("login") = 1
   Session.Item("userID") = txtId.Text
   Response.Redirect("http://www.noidellac.it/compiti/index2.aspx")
  End If
  objReader.Close()
  Con.Close()
 End Sub