Your issue is that you are mixing $_GET and $_POST.
See your code here, http://.../index.php?Email=<?php echo $_POST['Email']; ?>, when you post to that one, there will no longer be a $_POST['Email'], but a $_GET['Email']. So the first post will likely work (if you are using <form method="post" action="...">), but the second submit will fail, as $_POST['Email'] no longer exists.
So I recommend that you don't use parameters in the action. Instead, put them in a hidden field or switch to only $_GET parameters.
Option 1, use hidden field
Change the form on your second page to:
<form action="http://.../index.php" method="POST">
<input type="hidden" name="Email" id="Email" value="<?php echo $_POST['Email'];?>" />
...
</form>
Option 2, use only $_GET
Change the form on your first page to <form ... method="GET">
And then change the form on the second page to use $_GET['Email'] and the method to GET.
<form action="http://.../index.php??Email=<?php echo $_GET['Email'];?>" method="GET">
...
</form>
Option 3, Use $_REQUEST instead of $_POST
Simply use http://.../index.php?Email=<?php echo $_REQUEST['Email']; ?> as your action url, as $_REQUEST is a merge of $_GET and $_POST. Be aware that this is a merge of $_GET, $_POST and $_COOKIE.