Error :'WebForm_PostBackOptions' is undefined , what is causing?

Question

Hello I am learning ASP.NET and I am having some problems with getting data from the previous page to the present page. It gives the following error when I do so.

" Microsoft JScript runtime error: 'WebForm_PostBackOptions' is undefined "

I am using visual studio and the web-server is the one inbuilt with visual studio.

This is the code which seems to give the error.

  protected void Page_Load(object sender, EventArgs e)
  {
  if (PreviousPage != null)
  {
  lblInfo.Text = "You came from a page titled " +
  PreviousPage.Title + "<br />";
  //CrossPage1 prevPage = PreviousPage as CrossPage1;
  CrossPage1 prevPage = PreviousPage as CrossPage1;
  if (prevPage != null)
  {
  lblInfo.Text += "You typed in this: " + prevPage.FullName;
  }
  }
  }
Can someone please help me. I am stuck with this error for days now having no success in finding a solution.
Thank you.