AJAX Post为一个函数提供了404错误，但类似的函数运行正常

Question

I am using jQuery and AJAX to run PHP functions without refreshing the page. It was working fine for my first two instances but I added a new one an now the new instance keeps giving me the following error

POST http://www.example.com/ajax.php 404 (Not Found)

I checked and rechecked and try to fin a similar error somewhere else by I am stumped. Here is my html

<img id="green" src="http://www.example.com/image/sign_no.jpg" onclick="runAjax(this.id)" />
<span id="blue" onclick="runAjax(this.id)">Press Here</span>

Here is my jQuery code

<script language="javascript">
    function runAjax(id) {
        if (id == "green") {
            if (document.getElementById("green").src == "http://www.example.com/image/sign_no.jpg") {
                document.getElementById("green").src = "http://www.example.com/image/sign_yes.jpg";
                $.ajax({
                    type: "POST",
                    url: "/ajax.php",
                    data:{action:"green_pressed",user_id:"' . $user_id . '"},
                    success:function(html) {
                        alert(id);
                    }
                });
            }
        }
        else if (id == "blue") {
            $.ajax({
                type: "POST",
                url: "/ajax.php",
                data:{action:"blue_pressed",run_id:"' . $run_id . '"},
                success:function(html) {
                    alert(id);
                }
            });

        }
    }
</script>

This is the ajax.php file

if($_POST['action'] == 'green_pressed') {
        print_r($_POST['user_id']);
}
if($_POST['action'] == 'blue_pressed') {
        print_r($_POST['run_id']);
}

So when I press the green id there is no issues, the code runs fine but when I press the blue id there is where I get the error. Any insights?