Why doesnt this code update the db?? <option>

I get to the webhoster’s ERROR 404 page..

[code=php]

if(isset($_POST[‘submit’]))
{
include_once ‘dbcon.php’;

$abc= mysqli_real_escape_string($_POST[‘abc’]);

mysqli_query($con, “UPDATE users SET abc=’$abc’ WHERE username='”.$_SESSION[‘user’].”‘ “);

}

[/code]

[code=html]
<form action=”” method=”post”> //action is in same file
<select name=”abc”>

<option value=”a” <?php if ($value == “a”) {echo ” selected”;} ?> >a</option>
<option value=”b” <?php if ($value== “b”) {echo ” selected”;} ?> >b</option>
<option value=”c” <?php if ($value== “c”) {echo ” selected”;} ?> >c</option>
<option value=”d” <?php if ($value== “d”) {echo ” selected”;} ?> >d</option>

</select>

<button type=”submit” name=”submit” > ok</button>
</form>
[/code]

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