static controls disappearing in runtime

I created a master page and 2 content forms, but in both forms the controls disappear when I click a button to save data

Bellow the html code from master page and content form:
 
Master Page

<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
    <link href="App_Themes/Temas/gtvb.css" rel="stylesheet" type="text/css" />
</head>
<body>
    <form id="form1" runat="server">
    &nb ...