shrugs My IE cached the results for me, so that when I clicked "Back" it kept the 'PHP TEST' value.
A simple solution, instead of sessions, would be to echo the form again instead of a back button. Near the top, but some nice big text that stands out saying "Error! You did something wrong! Bwhahaha, no free book for j00!" (or something similar 😉).
That way, when you echo the form, you can do it like so:
<td><input type="text" name="email_address" size="40" value="<?PHP echo $_POST['email_address']; ?>"></td>
and so on, so that PHP echo's out the data they sent, including the erranous data so that they have a chance to make corrections/modifications.