$ .ajax POST问题

I have a big issue with $.ajax. I try to send a file name to the PHP part (in the same file), to help me stocking that name in a $_SESSION. It worked perfectly yesterday, but not anymore. Is there a browser issue instead of code issue ? Here is my code :

JS function

<script type="text/javascript" charset="utf-8">

function no_select(){
    var images = $("#selected_images").text();
    if(images != ''){
        var tmpFile = $("#selected_images").text();
        var arrayFile = tmpFile.split(",");
        if (arrayFile.length > 2){
            alert("Il ne faut selectionner qu'un seul badge !");
            return false;
        }
        var value = $.ajax({
            type: "GET",
            dataType: "json",
            url: "overview_list.php",
            data: "selectedImage="+arrayFile[0],
            async: false,
            success: function()
            {
            return true;
            }
        });

        return true;
    } else if(images == ''){
        alert("Il faut selectionner un badge");
        return false;
    }       
}

</script>

PHP

<?php
if(!empty($_GET['selectedImage'])){
    $let = $_GET['selectedImage'];
} else {
    $let = "";
}

$_SESSION['selectedImage'] = $let;
?>

I have already check a lot of solutions around the web, but there was no solution for me.

It should be like

$.ajax({
                  type: "GET",
                  dataType: "json",
                  url: "overview_list.php",
                  data: {selectedImage:arrayFile[0]},
                  async: false,
                  success: function()
                  {
                    return true;
                  }

and makesure arrayFile[0] is getting value