you see, your variables $_POST['whatever'] on thankyou4.php are not valid anymore when the header location changes pages
in order to pass the variables, you could move all the form processing code over to thankyou4.php, change a few things in the processing to fit of course, and set your <form action="thankyou4.php">.
OR
you could create a session using the variables posted and kill them after they are displayed on thankyou4.php
with your system, i would just do something like this using explode:
//on your first page..
$string = $var1.":".$var2.":".$var3;
$_SESSION['registerinfo'] = $string;
header("Location: thankyou4.php");
//and here on thankyou4.php
$registerinfo = $_SESSION['registerinfo'];
$info = explode(":", $registerinfo);
echo $info[0]; //var1 from your prev page
echo $info[1]; //var2 from your prev page
echo $info[2]; //var3 from your prev page
when submitted and there are no problems, a string with the registration information is created (seperating each one with the character ':') and a session is started with the string.
then the location is changed and you explode the session information into the array $info, and you can echo them out as so..
thats probably how i would go about it,
good luck