WML - What is "HTTP Error: 411 Length Required"?

<?php

?>
<?xml version="1.0"?> 
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"  
"http://www.wapforum.org/DTD/wml_1.1.xml">
 
<wml>
<card id="card1" title="Login">
<p mode="wrap">

Enter username and password to log in.<br/>
Username
<input name="username" type="text"></input><br/>
Password
<input name="password" type="password"></input>

<do type="accept" label="Login"> 
<go href="password2.php" method="post"> 
</go> 
</do>
</p>
</card>

</wml>

<?php

?>
<?xml version="1.0"?> 
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"  
"http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>
<card id="card2" title="Welcome">

<?php
//print_r($_POST);

$username = $_POST['username'];
$password = $_POST['password'];
echo $username;
echo $password;
$HitError = "false";

if (empty ($username))
{
echo ("You did not enter a username, please go back and try again.<br>");
$HitError = "true";
}
?>

</card>
</wml>

<postfield name="password" value="$(password)"/> 
<postfield name="username" value="$(username)"/>