How do I get a WebMethod to be enacted from an Ajax Command

"Error Code: [object Object]"

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
    <script type="text/javascript">
        function GetDateTime() {
            $.ajax
            ({
                type: "POST",
                url: "Default.aspx/GetServerDateTime",
                data: {'one':'1'},
                contentType: "application/json;charset=utf-8",
                dataType: "json",
                success: function (result) {
                    alert(result.d);
                },
                error: function (err) {
                    alert("Error Code: " + err);
                }
            });
        }
    </script>

protected void Button1_Click(object sender, EventArgs e)
{
    ScriptManager.RegisterClientScriptBlock(this, this.GetType(), "scr", "Javascript:GetDateTime();", true);
}
[WebMethod]
public static string GetServerDateTime()
{
    string date = DateTime.Now.ToString();
    return date;
}