PHP POST标头不适用于子域

Question

I am a facing a wired issue. On my sub-domain i have PHP script, that works fine till few days ago.. but now it is not working.

It use _POST data, i submit post data but it don't getting any post data.

So, for testing i am using this code:

<?php
if (isset($_POST['Code'])){
    echo 'set';
} else {
    echo 'not set';
}

echo '<br>';
exit ('911');
?>

and here is the HTML form for testing:

<form method="POST" action="http://MySubDomain.MyDomain.com/chk.php" name="Test">
    <input name="Code" value="varData"/>
    <p align="center">
        <input type="submit" value="Send Request To Server !"/> 
    </p>    
</form> 

but it's not working above php code returns:

not set
911

but if i run that same php file from my base domain and submit the request it works fine and returns:

set
911

i m in so danger.. as that sub domain process a important script for my site. and now it is not working while it was working fine few days ago..