Internal Server Error: 500 when code make a URL - http-status-code-500

Question

When my PHP script creates a URL like: ..../recover.php?success then create an error:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at webmaster#testlogin.muhammadmasud.info to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.
MY script `
?>
<p>Thanks, we have emailed you.</p>
<?php
}else{
$mode_allowd = array('username', 'password');
if(isset($_GET['mode']) === true && in_array($_GET['mode'], $mode_allowd) === true){
if(isset($_POST['email']) === true && empty($_POST['email']) === false){
if(email_exists($_POST['email']) === true){
Recover($_GET['mode'], $_POST['email']);
header('location: recover.php?success');
exit();
}else{
echo '<p style="color:red">Oops, we could not find that email address!</p>';
}
}
?>
<form action="" method="post">
<table style="boder:none">
<tr>
<td>Please enter your email address:</td>
</tr>
<tr>
<td><input type="text" name="email"></td>
</tr>
<tr>
<td><input type="submit" value="Recover"></td>
</tr>
</table>
</form>
<?php
}else{
header('location: index.php');
exit();
}`