how to call protected mathod.

I Hop You Under Stand By Example

Public Class QueryBuilder
    Inherits System.Web.UI.Page

Protected Sub ValidateDate(ByVal sender As Object, ByVal e As ServerValidateEventArgs)
      If Regex.IsMatch(txtdated.Text, "(((0|1)[1-9]|2[1-9]|3[0-1])\/(0[1-9]|1[1-2])\/((19|20)\d\d))$") Then
          Dim dt As DateTime
          e.IsValid = DateTime.TryParseExact(e.Value, "dd/MM/yyyy", New CultureInfo("en-GB"), DateTimeStyles.None, dt)
          If e.IsValid Then
              ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Valid Date.');", True)
          End If
      Else
          e.IsValid = False
      End If
  End Sub

Protected Sub btnstudent_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnstudent.Click
 Dim cs As New QueryBuilder
cs.ValidateDate()

End Sub

End Class

By definition, you can only call a protected method from the declaring class or any of derived classes.
Strictly speaking, there is another way, reflection, but: 1) this is a trick; 2) you should not get to such advanced topics before you make yourself confident with the fundamentals, which you don't know yet.

Please read: http://msdn.microsoft.com/en-us/library/76453kax.aspx[^].

Please, don't ask what to do if you cannot use such a derived class or the declaring class. The answer would be: the decision is up to you. It's possible that you should not use the protected method, or even need to radically fix your code design. Anyway, your related follow-up questions will be welcome.

—SA