ASP.NET Navigation and Validation quesitons

Two things I am trying to figure out.

Question 1.
A site map comes from the master page.  The site map is displayed in a tree view.  How can I disable the tree view until there are no more pages errors.

Question 2.
Both the current and prior page use  MasterPageFile="~/Site.Master"
And
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1"

Page 1 has a control named TextBox1.

Why does this PageLoad() code never find control TextBox1?
{
   ContentPlaceHolder cp = ((ContentPlaceHolder)PreviousPage.Master.FindControl("ContentPlaceHolder1"));
           string fname = ((TextBox)cp.FindControl("TextBox1")).Text;
           valuesFromPriorPage.Text = fname;
}


Thanks