Unknown fault in php code

Question

Sorry for having such a useless question on such a helpful website but I've been having trouble with this so much and I tried everything I could find but nothing worked so here I am on stack-overflow asking stupid questions. So I get an error in my php code but I can't seem to understand what is the problem. Here is the code:

<?php
session_start();
$username = $_POST['user'];
$password = $_POST['pass'];
function fnEncrypt($sValue, $sSecretKey)
{
    return rtrim(
        base64_encode(
            mcrypt_encrypt(
                MCRYPT_RIJNDAEL_256,
                $sSecretKey, $sValue, 
                MCRYPT_MODE_ECB, 
                mcrypt_create_iv(
                    mcrypt_get_iv_size(
                        MCRYPT_RIJNDAEL_256, 
                        MCRYPT_MODE_ECB
                    ), 
                    MCRYPT_RAND)
                )
            ), "\0"
        );
}
function fnDecrypt($sValue, $sSecretKey)
{
    return rtrim(
        mcrypt_decrypt(
            MCRYPT_RIJNDAEL_256, 
            $sSecretKey, 
            base64_decode($sValue), 
            MCRYPT_MODE_ECB,
            mcrypt_create_iv(
                mcrypt_get_iv_size(
                    MCRYPT_RIJNDAEL_256,
                    MCRYPT_MODE_ECB
                ), 
                MCRYPT_RAND
            )
        ), "\0"
    );
}

$con = mysqli_connect("localhost", "root", "youcantknowthis", "Iprefernottotellthedbname");
$sql = "select * from Users where Username like '$username' and Password like '$password'";
$result = mysqli_query($con, $sql);
$chrow = mysqli_fetch_assoc($result);
if($chrow['Username'] == $username)
{   
    $mrand = pseudo_random_bytes(30);
    $_SESSION['token'] = fnEncrypt($mrand, "G3%*&IIQ|\/<HlOp:@hiuyLd$*%%!¬\"\"'gR@@:f.jr&");
    $_SESSION['user'] = fnEncrypt($username, fnEncrypt($password, $mrand));
    $_SESSION['password'] = fnEncrypt($password, "DJs%73&%38fKDj5&£$8djJ^:LJHG{@l''k}@::@\"fdshj%\"\"\\\\:GFkkdH:gf~?.'*&^%$$$5fhd");
    echo '<script>parent.location = "http://localhost/BadenBad/";</script>';    
}
else
{
    echo "Login incorrect";
}
?>

So this is basically a php server-side script for logging in. As you may have guessed from the code it is nested in an iframe though it isn't put directly into the iframe. Rather the other html website nested in the iframe (the one that calls the php script). As an explanation of what exact problem do I encounter, well I don't exactly know but when I remove the lines starting from $_SESSION['something']=... everything works fine (except no login process happens ofcourse). Just as a hint for what kind of error to search for I know for fair and square that It is not a problem with the following: 1. PHP Database Access 2. Sessions (they work okay) But I very strongly suspect it is a problem with the functions (fnEncrypt and fnDecrypt). Anyway sorry for the stupid question and long post and please scan the code and try to find some mistakes. Im sorry you can't test the code as there are numerous other files required to test this one script. Thank you in advance!. (Small edit) When I run the script it sort of crashes and never reaches the stage when it calls echo and redirects.