jQuery works only half the time
<?php
$data = mysql_query("SELECT * FROM Contests");

while($row = mysql_fetch_array( $data )){
$query = mysql_query("SELECT * FROM userContests WHERE userID='$userID' AND contestID='$row[contestID]';") or die(mysql_error());
$checked = mysql_fetch_assoc($query);
?>

<script type="text/javascript">
$(document).ready(function() {
    var checked = <?php echo $checked['value']; ?>;
    var postID = <?php echo $row['postID']; ?>;
    var userID = <?php echo $current_user->ID; ?>;

    if (checked == 1) {
        $('#post_<?php echo $row['postID']; ?>').addClass('like');
    } else if (checked == 0) {
        $('#post_<?php echo $row['postID']; ?>').addClass('dislike');
    }

    $('#like_<?php echo $row['postID']; ?>').click(function(liked) {

        $.ajax({
            url: 'check.php',
            type: 'POST',
            data: 'userID=' + userID + '&postID=' + postID + '&value=' + '1',
            success: function(result) {
                $('#Message_<?php echo $row['postID']; ?>').html('').html(result).prependTo('#post_<?php echo $row['postID']; ?>');
            }
        });

        $('#post_<?php echo $row['postID']; ?>').removeClass('dislike').addClass('like');
        if (showLikes.attr('checked')) {
            $('#post_<?php echo $row['postID']; ?>').toggle();
        }
    });

    $('#dislike_<?php echo $row['postID']; ?>').click(function(disliked) {

        $.ajax({
            url: 'check.php',
            type: 'POST',
            data: 'userID=' + userID + '&postID=' + postID + '&value=' + '0',
            success: function(result) {
                $('#Message_<?php echo $row['postID']; ?>').html('').html(result).prependTo('#post_<?php echo $row['postID']; ?>');
            }

        $('#post_<?php echo $row['postID']; ?>').removeClass('like').addClass('dislike');
        if (showDislikes.attr('checked')) {
            $('#post_<?php echo $row['postID']; ?>').toggle();
        }
    });

<div id="post_<?php echo $row['postID']; ?>" class="post">
<div id="post_<?php echo $row['postID']; ?>_inside">
    <div>
        <a id="like_<?php echo $row['postID']; ?>" class="like" href="#"><span></span></a>
    </div>
    <div>
        <a id="dislike_<?php echo $row['postID']; ?>" class="dislike" href="#"><span></span></a>
    </div>
    <b><?php echo $row['Title']; ?></b><br>
    Expires: <?php echo $row['Exp']; ?><br>
    <ul id="listM"></ul>
</div>
</div>
<div id="Message_<?php echo $row['postID']; ?>" class="reminder"></div>

<?php
}
?>

a.like {
float: right;
background: url(images/entered.png) no-repeat top center;
height: 30px;
width: 28px;
}

a.like:active {
float: right;
background: url(images/entered.png) no-repeat bottom center;
height: 30px;
width: 28px;
}

a.dislike {
float: right;
background: url(images/not-interested.png) no-repeat top center;
height: 30px;
width: 28px;
}

a.dislike:active {
float: right;
background: url(images/not-interested.png) no-repeat bottom center;
height: 30px;
width: 28px;
}