Special Characters Validation

    Sub FnUserInput(sender as Object, args as ServerValidateEventArgs)
     Dim txtInput As String = Me.TxtUser.Text.Trim
     Dim txt
     txt = ""
     Dim c
     Dim P
     Const o = "~!@#$%^&*()_+=-`:""" & "<>?;,./{}[]|\*" & "'" & " "
     For i As Integer = 1 To Len(txtInput)
      c = Mid(txtInput, i, 1)
      P = InStr(o, c)
      If P > 0 Then
       args.IsValid = False
      End If
     Next
   End Sub