Infopath arraylist property

Hi, I want to create an ArrayList property in an Infopath form. When I try to add values to the property I get "The name 'xxxxx' does not exist in the current context". Any help please? thanks

PROPERTY

        private ArrayList Xxxxx
        {
            get
            {
                ERROR >>> return xxxxx;
            }
            set
            {
                ERROR >>> xxxxx = value;
            }
        }

        public void FormEvents_Loading(object sender, LoadingEventArgs e)
        {
            try
            {
                ArrayList xxxxx = new ArrayList();
........

METHOD

        public void drpChantier_Changed(object sender, XmlEventArgs e)
        {
            try
            {
.......
                string qstrReferenceForm = FormState["_qstrReferenceForm"].ToString();

                Xxxxx.Add(qstrReferenceForm);
.......