title: Why I got this exception :Sys.WebForms.PageRequestManagerServerErrorException: Invalid postback or callback argument
body: <p>Why I got this error </p>
  
  <pre><code>Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: Invalid postback or callback argument.  Event validation is enabled using &lt;pages enableEventValidation="true"/&gt; in configuration or &lt;%@ Page EnableEventValidation="true" %&gt; in a page.  For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them.  If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.
  </code></pre>
  
  <p>this error appears when the event for Save command is started </p>
  
  <pre><code>  Protected Sub DataList1_ItemCommand(source As Object, e As System.Web.UI.WebControls.DataListCommandEventArgs) Handles dlMainTraing.ItemCommand
          If e.CommandName = "Save" Then
              Dim lblMainId = CType(dlMainTraing.Items(e.Item.ItemIndex).FindControl("Train_M_IndxLabel"), Label)
              Dim txtSubTrainingName2 = CType(dlMainTraing.Items(e.Item.ItemIndex).FindControl("txtSubTrainingName"), TextBox)
              Dim a = addSubTraining(CInt(lblMainId.Text), txtSubTrainingName2.Text)
              ' Dim gvSubTraning As GridView = CType(e.Item.FindControl("gvSubTraning"), GridView)
              'gvSubTraning.DataBind()
          End If
  
      End Sub
  </code></pre>