Ajax事件始终重定向

I have a button with an action :

<a id="viewlog" href="" class="btn btn-default" />

And :

$("#viewlog").bind('click', function (e) {
    $.ajax({
        url: "/Log/FindFile?idTraitement=" + $("#IdTraitement").val(),
        success: function (data) {
            if(data.success == false){
                Lobibox.alert('error', { title: 'Erreur', msg: 'Fichier introuvable' });     
            }
            else
                window.location.href = "/Log/GetTraitementLogs?idTraitement=" + $("#IdTraitement").val();
        },
        error: function (response) {
            Lobibox.alert('error', { title: 'Erreur', msg: response.responseText });
        }
    });
});

The action call is this, the idea is if a file is found I return true else false :

public JsonResult FindFile(int idTraitement)
{
    string filename = string.Empty;

    try
    {
        filename = new QryTraitementService().GetErrLogFilename(idTraitement);
    }
    catch(Exception e)
    {
        return Json(new { success = false, responseText = e.Message }, JsonRequestBehavior.AllowGet);
    }

    return Json(new { success = true }, JsonRequestBehavior.AllowGet);
}

and then, if the file is found :

public FileResult GetTraitementLogs(int idTraitement)
{
    string filename = new QryTraitementService().GetErrLogFilename(idTraitement);

    return File(filename,"text/csv",filename);
} 

So, first thing is when I come back to client side with firefox or chrome I go to the error in ajax but with IE I go to the success with a var success in data.

But the big problem is that the function always redirect me to nowhere so I fail in 404. Why the call always redirect me ? Even if I don't pass on a window.location.href ?