problems with $_POST returning NULL values in php 4.4.2

[RDizzle]

okay. so all i am doing is changing a registration script that uses
$_GET to a script that uses $_POST, but the validation script now
returns NULL values for all posted vars.

What's the deal?

NOTE: when i use $_GET the script just works.

Thanks in advance for helping a noob.

script with the form:
<?php
// Connect to a session
session_start( );
?>
<form method="POST" action="reg_validate.php">
<h2>User Profile</h2>
<?php

// Show meaningful instructions for UPDATE or INSERT or errors
if(empty($errors))
{
if (session_is_registered("loginUsername"))
{
echo "<p><b>Please update your profile below as
needed:</b></p>";
}
else
{
echo "<p><b>Please fill in all details below to
join.</b></p>";
}
}else{
// Display error message to the user
showMessage();
}
?>
<table>
<col span="1" align="right">

<tr><td>User Name:</td>
<td><? echo fieldError("userName", $errors); ?>
<input type="text" name="userName"
value="<? echo $formVars["userName"]; ?>"
size=25></td>
</tr>

<tr><td>Real Name:</td>
<td><? echo fieldError("realName", $errors); ?>
<input type="text" name="realName"
value="<? echo $formVars["realName"]; ?>"
size=25></td>
</tr>

<tr><td>Sex:</td>
<td><select name="title">
<option <?php if ($formVars["sex"]=="M")
echo "selected";?>>M
<option <?php if ($formVars["sex"]=="F")
echo "selected";?>>F
</select><br></td>
</tr>

<tr><td>City:</td>
<td><? echo fieldError("city", $errors); ?>
<input type="text" name="city"
value="<? echo $formVars["city"]; ?>"
size=20></td>
</tr>

<tr><td>State:</td>
<td><? echo fieldError("state", $errors); ?>
<input type="text" name="state"
value="<? echo $formVars["state"]; ?>"
size=20></td>
</tr>

<tr><td>Zipcode:</td>
<td><? echo fieldError("zipcode", $errors); ?>
<input type="text" name="zipcode"
value="<? echo $formVars["zipcode"]; ?>"
size=5></td>
</tr>

<tr><td>Country:</td>
<td><? echo fieldError("country", $errors); ?>
<input type="text" name="country"
value="<? echo $formVars["country"]; ?>"
size=5></td>
</tr>

<tr><td>Date of birth (dd/mm/yyyy): </td>
<td><? echo fieldError("dob", $errors); ?>
<input type="text" name="dob"
value="<? echo $formVars["dob"]; ?>"
size=10></td>
</tr>

<?php
// Only show the username/email and password
// <inputwidgets to new users
if (!session_is_registered("loginUsername"))
{
? <tr><td>Email:</td>
<td><? echo fieldError("email", $errors); ?>
<input type="text" name="email"
value="<? echo $formVars["email"]; ?>"
size=50></td>
</tr>

<tr><td>Password:</td>
<td><? echo fieldError("loginPassword", $errors); ?>
<input type="password" name="loginPassword"
value="<? echo $formVars["loginPassword"]; ?>"
size=8></td>
</tr>

<tr><td><img src="/captcha.php"></td>
<td><? echo fieldError("loginCaptcha", $errors); ?>
Type in the text from the image to the left<br/>
<input type="text" name="loginCaptcha"
value="" size=8></td>
</tr>

<?php
}
?>
<tr>
<td><input type="submit" value="Submit"></td>
</tr>
</table>
</form>
<?php
foot();
//prevent session hijacks by clearing sessions once
informations is
displayed
// Clear the formVars so a future <formis blank
session_unregister("formVars");
session_unregister("errors");
?>

validation snippet:
(not including all the validation just the meat where the vars are
being grabbed)

<?php
// Initialize a session
session_start();

// Register an error array - just in case!
if (!session_is_registered("errors"))
session_register("errors");

// Clear any errors that might have been
// found previously
$errors = array();
$formVars = array();

// Set up a $formVars array with the POST variables
// and register with the session.
if (!session_is_registered("formVars"))
session_register("formVars");

// TO DO remove $HTTP_GET_VARS and use all $_GET variables
// TO DO use $_POST
$formVars["userName"] = clean($_POST["userName"],50);
$formVars["realName"] = clean($_POST["realName"], 50);
$formVars["sex"] = clean($_POST["sex"], 50);
$formVars["city"] = clean($_POST["city"], 50);
$formVars["state"] = clean($_POST["state"], 50);
$formVars["zipcode"] = clean($_POST["zipcode"], 50);
$formVars["country"] = clean($_POST["country"], 50);
$formVars["dob"] = clean($_POST["dob"], 50);
$formVars["email"] = clean($_POST["email"], 50);
$formVars["loginPassword"] = clean($_POST["loginPassword"], 50);
$formVars["loginCaptcha"] = clean($_POST["loginCaptcha"], 50);

....
?>

[RDizzle]

figured out a workaround for $_POST

instead of calling $_POST while assigning to my session array
$form_vars like this:
$formVars["userName"] = clean($_POST["userName"],50);

i call $_POST to a normal var $userName like this:
$userName = $_POST["userName"];

then do
$formVars["userName"] = clean($userName,50);

however, this does not explain why
$formVars["userName"] = clean($_GET["userName"],50);

works when using get method while
$formVars["userName"] = clean($_POST["userName"],50);

doesn't when using post method.

so flummoxed,
raymond