Windows phone app with sqlite local storage

I'm trying to save my objects that I got back from my JSON into a local storage db with SQLite

I've imported a lot of packages and also the SQLite framework.

I've also made these two classes: Activity

public class Activity : INotifyPropertyChanged
    {
        [SQLite.PrimaryKey, SQLite.AutoIncrement]
        public int act_id
        {
            get;
            set;
        }
        //The Id property is marked as the Primary Key
        private int act_organization_id_value;
        private int act_creator_id_value;
        private int act_free_value;
        private int act_subcription_value;
        private int act_external_value;
        private int act_active_value;
        private int act_future_value;
        private int act_status_value;
        private int act_viewed_value;
        private string act_location_value = String.Empty;
        private string act_lng_value = String.Empty;
        private string act_title_value = String.Empty;
        private string act_information_value = String.Empty;
        private string act_type_value = String.Empty;
        private string act_color_value = String.Empty;
        private string act_event_identifier_value = String.Empty;
        private DateTime act_start_value = DateTime.Now;
        private DateTime act_end_value = DateTime.Now;

         [OneToMany(CascadeOperations = CascadeOperation.All)]
        public List<ActivityMember> membrs { get; set; }

       //Other getters and setters
}

Activity members

   public class ActivityMember : INotifyPropertyChanged
    {
        [SQLite.PrimaryKey, SQLite.AutoIncrement]
        public int mem_id
        {
            get;
            set;
        }

        private int mem_activity_id_value;
        private int mem_organization_id_value;
        private int mem_role_id_value;
        private int mem_creator_value;
        private int mem_accepted_value;
        private int mem_activity_accepted_value;
        private int mem_active_value;
        private int mem_deleted_value;
        private string mem_profile_color_value = String.Empty;
        private string mem_picture_value = String.Empty;
        private string mem_email_value = String.Empty;
        private string mem_phone_value = String.Empty;
        private string mem_gsm_value = String.Empty;
        private string mem_address_value = String.Empty;
        private string mem_postal_value = String.Empty;
        private string mem_city_value = String.Empty;
        private string mem_country_id_value = String.Empty;
        private string mem_first_name_value = String.Empty;
        private string mem_last_name_value = String.Empty;
        private string mem_extra_info_value = String.Empty;
        private string mem_street_value = String.Empty;
        private string mem_streetnumber_value = String.Empty;
        private string mem_gender_value = String.Empty;
        private DateTime mem_birthdate_value = DateTime.Now;

        [ManyToOne]      // Many to one relationship with Activity
        public Activity activity { get; set; }

        // all other getters and setters
}

An activty can have more ActivityMembers. When I build and run I get the following error:

When I debug I found out that it is caused by the following lines: In Activity:

   [OneToMany(CascadeOperations = CascadeOperation.All)]
        public List<ActivityMember> membrs { get; set; }

In activityMember:

  [ManyToOne]      // Many to one relationship with Activity
    public Activity activity { get; set; }

Any help on how correctly doing this?